Creating calculations for a online form

Hi,
 
I´m a first time user of acrobat and I´m trying to make an online form for our little company. I´ve got the basic form made and the fields opened but I can´t figure out how to make the calculations for the form.
 
Can someone help with this?
 
Address:
Date:
Order Ref:
Reference code
Description / Design Title
Size
 
This is the parts I need the calculations for: and how do I separate each row for different items?)
Qty (Qty multiplied with Price (Euro) )
Price (Euro) (Qty multiplied with Price (Euro) = Amount
Amount
Sub Total (Amounts for each lined added up to give Subtotal)
IVA (16%) (Subtotal multiplied by tax percentage of 16%)
Total of everything
  
Thanks!