I can't really tell what your formula says.

I used the following amortization formula found Here.

, where

where

A= payment Amount per period (monthly periods)P= initial Principal (loan amount)r= interest rate per period (yearly rate / 12)n= total number of payments or periodsA= payment per month

P= 26,000

r= 4.9% per year / 12 months = %

n= 60 monthly periods