Newbie visual basic 6 - vb6

Question

Private Sub Command1_Click()
Select Case used.Text
Case Is <= 30
pay = used * 120
Case Is > 30, Is <= 60
pay = used * 150
Case Is > 60, Is <= 90
pay = used * 190
End Select
EX:
MR.A used 75m3 of water a month so he must pay:
30 x 120 = 3600
30 x 150 = 4500
15 x 15 = 2850
and total : 10950
but my code doesnt right help me fix it im newbie

Answer 1

i'm also a newbie, sure this is a horrible way to code it but it seems to work...first off replace literals with variables to allow for changing requirements. I didn't check many cases so this might not be exact but was fun to think thru the problem.
Private Sub Command1_Click()
Dim pay As Double
Dim used As Double
Dim balance As Double
Dim BillingIncrement As Double
Dim FirstUnitPrice As Double
Dim SecondUnitPrice As Double
Dim MaxUnitPrice As Double
BillingIncrement = 30
FirstUnitPrice = 120
SecondUnitPrice = 150
MaxUnitPrice = 190
'put in loop to test various inputs for debug only
For used = 10 To 100 Step 5
Debug.Print "used ", used
If used <= BillingIncrement Then
pay = used * FirstUnitPrice
Else
pay = BillingIncrement * FirstUnitPrice
Debug.Print "first " & BillingIncrement & " units billed at 120"
balance = used - BillingIncrement
Debug.Print "balance ", balance
If balance > BillingIncrement Then
pay = pay + BillingIncrement * SecondUnitPrice
Debug.Print "second " & BillingIncrement & " units billed at " & SecondUnitPrice
balance = balance - BillingIncrement
If balance > 0 Then
pay = pay + balance * MaxUnitPrice
Debug.Print balance, " units billed at " & MaxUnitPrice
End If
Else
Debug.Print balance, " billed at " & SecondUnitPrice
pay = pay + balance * SecondUnitPrice
End If
End If
Debug.Print "Pay = ", pay
' a couple example test cases
If used = 40 Then
If pay <> 5100 Then
Debug.Print "error"
Else: Debug.Print "ok so far"
End If
End If
If used = 60 Then
If pay <> 8100 Then
Debug.Print "error"
Else: Debug.Print "ok so far"
End If
End If
'reset for next loop
pay = 0
balance = 0
Next
End Sub