VB 2005 Express Edition Calculation?

I am trying to make a VB User Interface with Visual Basic Express Edition 2005 where clients can do the following calculation: Stranding x Bare Copper CMA = Total CMA

I have created an access 2007 database called Total_CMA, this database has 2 columns, one with the SIZE and the other AREA, but in this database the Size = Area ( was not sure how to set that up properly ) so I left it at 2 columns and then went to VB and set up with a listbox for the Size and have bound the database to this listbox, and when I debug it, the numbers for Size show up in the listbox, so thats looking good so far, since the size = area when I bound it it asked to get and I picked Size then it asked value equals so I picked Area and hope that was the proper thing to do.

I added a TEXTBOX named STRANDS for the customer to input the number of strands, then a button to click to calculate total CMA and another Textbox named TOTAL to display the results. All have labels next to them naming what they are.

My question is, how do I get what the customer selects in the listbox to multiply by the STRANDS textbox and output in the TOTAL textbox when clicked on the button to calculate total CMA. I also need to make sure whatever SIZE they picked in the listbox is going to take the AREA number ( not the SIZE number ) and multiply it by the STRANDS textbox.