A bond with exactly four years until maturity paying 6% p.a. coupons semi-annually and with a face value of $100 was purchased at a yield of 5% p.a. The bond was sold exactly two years later for a yield of 4.50% p.a. All coupons were reinvested at 4.75% p.a. Calculate the investment yield on this bond.

This question has me stumped. Any Help greatly appreciated.
Thank you.