Please provide solution with a detailed explanation and calculation process 

a. What is term structure of interest rates? How does liquidity preference theory explain the upward sloping term structure of interest rates compared to the expectations theory?

b. The 6-month, 12-month, 18-month, and 24-month zero rates are 4%, 4.5%, 4.75% and 5% with semiannual compounding. What is the forward rate for the six-month period beginning in 18 months?