Please explain c part of this question in detail.

A mortgage for a condominium had a principal balance of $48,500 that had to be amortized over the remaining period of 7 years. The interest rate was fixed at 4.42% compounded semi-annually and payments were made monthly. a. Calculate the size of the payments. Round up to the next whole number b. If the monthly payments were set at $822, by how much would the time period of the mortgage shorten