The Grewals agreed to monthly payments on a mortgage of $336,000.00 amortized over 20 years. Interest for the first five years was 4.5% compounded semi-annually.

a. Determine the Grewals' monthly payments.

b. Determine the balance owing after the 5-year term.

c. Before renewing for another term of 5 years at 4.3% compounded semiannually, the Grewals make an additional payment of $12,000. If they keep the same monthly payments, by how much will the amortization period be shortened?