VB.NET call a button function - database

Question

How do i go about this code, I want to call amountpayable on the confirm purchase button but it says amount payable is not declared and I am having a hard time trying to pass the value from another function... Anyone knows a quick easy fix? I am not familiar with visual basic so if someone can share a light on this query I just want an easy one, one i can easily understand
Here is the code
Private Sub BtnAddOrder_Click(sender As Object, e As EventArgs) Handles BtnAddOrder.Click
Dim AddOns As String
Dim BlackPearl As String
Dim Oreo As String
Dim Nata As String
Dim CoffeeJelly As String
Dim CreamCheese As String
AddOns = " "
BlackPearl = " "
Oreo = " "
Nata = " "
CoffeeJelly = " "
CreamCheese = " "
If ChkBoxBlackPearl.Checked = True Then
AddOns = "Black Pearl"
End If
If ChkBoxOreo.Checked = True Then
AddOns = AddOns & "," & " Oreo"
End If
If ChkBoxNata.Checked = True Then
AddOns = AddOns & "," & " Nata De Coco"
End If
If ChkBoxCoffeeJelly.Checked = True Then
AddOns = AddOns & "," & " Coffee Jelly"
End If
If ChkboxCreamCheese.Checked = True Then
AddOns = AddOns & "," & " CreamCheese"
End If
Dim Payment As String
Payment = " "
If RbtnGcash.Checked = True Then
Payment = "Gcash"
End If
If RbtnDebit.Checked = True Then
Payment = "Debit Card"
End If
If RbtnCoins.Checked = True Then
Payment = "Coins.ph"
End If
If RbtnCash.Checked = True Then
Payment = "Cash"
End If
Dim DiscountRate As Double
If RbtnPWD.Checked = True Then
DiscountRate = 0.05
End If
If RbtnSenior.Checked = True Then
DiscountRate = 0.1
End If
If RbtnStudent.Checked = True Then
DiscountRate = 0.03
End If
If RbtnDiscountNone.Checked = True Then
DiscountRate = 0
End If
Dim Transaction As String
Transaction = " "
If RbtnDelivery.Checked = True Then
Transaction = "15"
End If
If RbtnWalkin.Checked = True Then
Transaction = "None"
End If
TxtTotalAddOn.Text = Val(TxtBlackPearl.Text) + Val(TxtOreo.Text) + Val(TxtNataDeCoco.Text) + Val(TxtCoffeeJelly.Text) + Val(TxtCreamCheese.Text)
Dim Total As Integer
Dim DiscountPrice As Double
Dim AmountPayable As Double
Total = Val(TxtTotalAddOn.Text) + Val(TxtSizeprice.Text) + Val(TxtDeliveryFee.Text)
DiscountPrice = Total * DiscountRate
AmountPayable = (Total - DiscountPrice) * Val(ComboQuantity.Text)
If AddOns.Length <> 0 Then
MessageBox.Show("********************************" + vbCr + "Troo Tea Ordering System" + vbCr + "********************************" + vbCr + "Choosen DRINK: " + ComboDrink.Text + vbCr + "********************************" + vbCr + "Quantity: " + ComboQuantity.Text + vbCr + "********************************" + vbCr + "Size: " + Sizename + vbCr + "********************************" + vbCr + "Price " + TxtSizeprice.Text + vbCr + "********************************" + vbCr + "AddOns: " + AddOns + vbCr + "********************************" + vbCr + "Total AddOns " + TxtTotalAddOn.Text + vbCr + "********************************" + vbCr + "Delivery Fee" + TxtDeliveryFee.Text + vbCr + "********************************" + vbCr + "Discount " + TxtDiscount.Text + vbCr + "Total " + Total.ToString + vbCr + "Amount Payable: " + AmountPayable.ToString + vbCr + "********************************" + vbCr + "*******************" + vbCrLf + "Thank You For Your Order" + vbCrLf + "*******************")
End If
TxtOrderDetails.Text = ("Customer Name: " + TxtCustomername.Text + vbCrLf + "Phone Number: " + TxtPhone.Text + vbCrLf + "Address: " + TxtAddress.Text + vbCrLf + "***********************************************************" + vbCrLf + "Choosen DRINK: " + ComboDrink.Text + vbCrLf + "Quantity: " + ComboQuantity.Text + vbCrLf + "Size: " + Sizename + vbCrLf + "Price: " + TxtSizeprice.Text + vbCrLf + "AddOns: " + AddOns + vbCrLf + "Total AddOns: " + TxtTotalAddOn.Text + vbCrLf + "Delivery Fee: " + TxtDeliveryFee.Text + vbCrLf + "Mode Of Payment: " + Payment + vbCrLf + "Discount Rate for Each Order: " + TxtDiscount.Text + vbCrLf + "Total Price Per Order: " + Total.ToString + vbCrLf + "Amount Payable: " + AmountPayable.ToString + vbCrLf + "***********************************************************" + vbCrLf + "Thank You For Your Order" + vbCrLf + "***********************************************************" + vbCrLf + "Date Of Transaction: " + DateTimePicker1.Text)
End Sub
Private Sub BtnConfirm_Click(sender As Object, e As EventArgs) Handles BtnConfirm.Click
End Sub
End Class

Answer 1

Since you can't modify the signature of an event handler, you won't be able to pass the variable from one handler to the other. Instead, declare the variable as a field within the class.
See additional comments added in the code below. I simply cut out some of the code you provided for brevity and shifted the declaration of the AmountPayable to outside of the sub it was originally declared in.
You can read more on variable scope here
Private AmountPayable As Double 'move this declaration outside of the sub
Private Sub BtnAddOrder_Click(sender As Object, e As EventArgs) Handles BtnAddOrder.Click
Dim Total As Integer
Dim DiscountPrice As Double
Total = Val(TxtTotalAddOn.Text) + Val(TxtSizeprice.Text) + Val(TxtDeliveryFee.Text)
DiscountPrice = Total * DiscountRate
'variable can be assigned here
AmountPayable = (Total - DiscountPrice) * Val(ComboQuantity.Text)
End Sub
Private Sub BtnConfirm_Click(sender As Object, e As EventArgs) Handles BtnConfirm.Click
MessageBox.Show("Your Total is $" & AmountPayable) 'variable can be accessed here
End Sub
End Class