Special calculation on a fillable form

I have an order form I'm creating for a client.  There's a quantity column, price each column, shipping column and total column.  User will input the quantity, along with some other info.  However, the quantity column has to x (times) the price each column + the shipping column to get the total.  (A1 * A2 + A3 = TOTAL).  How do I write up the calculation or script in Acrobat, or can it do this?