Shopping System - Selecting Print Or Audio Books

The user can select from either print or audio books and add to the shopping cart. The list box shows all items in the shopping cart. There is a 6%. sales tax on the total cost of the items in the shopping cart and a 2 dollars shipping charge per item in the shopping cart. to remove an item from the shopping cart, the user selects it in the list box and clicks the remove button. the subtotal, tax, shipping, an total fields should be adjusted accordingly.

To add one of the items in the list to the shopping cart, the user selects it and clicks the add book to cart button. to cancel the operation, the user clicks the cancel button. I am using a standard module to declare global variables. My file is attach I have the problem that everytime I add a new item, it will just add 2 and then I add another item and it add 2 it does not show the subtotal or the tax and shipping and the real total....

Module PriceCalcModule
'constants for Print
Public Const g_decDID_YOU_KNOW As Decimal = 11.95
Public Const g_decHISTORY_SCOTLAND As Decimal = 14.5
Public Const g_decLEARN_CALC As Decimal = 29.95
Public Const g_decFEEL_STRESS As Decimal = 18.5
[Code] .....