can somebody please help me solve these two questions. its very difficult for me.

thank you!

4. Microsoft is an AAA rated firm. It has a 16-year bond with an annual coupon rate of 4% paid semi-annually. The bond is selling for 105. a. What is the yield to maturity of this bond? b. The new Windows software has had abysmal sales, and as a result, the firm is downgraded to AA-rated. The yield to maturity on AA-rated bonds is 5% per year. What will be the price of the above bond after the downgrade? C. Calculate the percentage in bond price from part (a) to part (b). Why do you think the bond price changed by such a large percentage? 5. Consider a municipal bond issued by the state of Massachusetts. It is an 8-year bond with a coupon rate of 6% paid semi-annually. The bond is rated AA. Spalding is an AA-rated firm, and it also has an 8-year bond with a coupon rate of 6% paid semi-annually. The marginal tax for investors in the bond market is 40%. Suppose the annual yield to maturity of Spalding's bond is 6%. What is likely to be the price of both bonds (State of Massachusetts and Spalding)