I can't seem to figure out how the calculation of a payment for my new vehicle is calculated. If anyone can help me here.

Loan: 28,131.85
Biweekly payment amount: 239.83
Interest Rate: 13.5
7 years
Contract Date: Jan 14, 2014
Contract End Date: Jan 1, 2021
First Payment Date: Jan 24, 2014
Simple Interest Loan

I can't seem to get to the payment of 239.83. I am looking for help with a formula to help me understand how this payment was calculated.