how do you calculate amortization

There are slightly different formulas depending on your exact question.

To find the amount of money that you must pay per period to pay back a loan, use this formula:

A  =  [P·r(1 + r)^n] / [ (1 + r)^n - 1]

where:  A = payback amount per period

             P = initial loan amount

             r = interest rate per period           (example 9% per year rate paid monthly:  0.09/12)

             n = total number of payments      (example: monthly payments for 8 years:  12·8)

If all that you want is an answer, you may try this site:  http://www.amortization-calc.com/