An investor is considering the purchase of an existing closed mortgage that was written 20 months ago

Question:

An investor is considering the purchase of an existing closed mortgage that was written 20 months ago to secure a $45,000 loan at 10% compounded semiannually paying $500 per month for a 4-year term. What price should the investor pay for the mortgage if she requires a semiannually compounded rate of return on investment of
a. 11%?
b. 10%?
c. 9%?