The answer to the following question is $13,791.60. I would like to know what formulas to use and in what order to arrive at this answer. thanks.

A person purchased a $131,637 home 10 years ago by paying 15% down and signing a 30 year mortgage at 9% compounded monthly. Interest rates have dropped and the owner wants to refinance the unpaid balance by signing a new 30 year mortgage at 5.4% compounded monthly. How much interest will refinancing save? (round to the nearest cent as needed)