what formula is used for these 2 questions? can you explain and show the solutions to both. thanks

2. Calculate the Duration of a 100 four-year 8% coupon bond when the market interest rate (YTM) is 6%. The bond pays interest annually. Using the calculated duration estimate the approximate change in the bond price if the market interest rate increases to 7% Explain how the duration of a bond is affected by the coupon rate. What does this relationship tell you about the link between a bond's coupon and its interest rate sensitivity? 2. Calculate the Duration of a 1,000 four-year 3.5% coupon bond when the market interest rate (yield to maturity) is 4%. The bond pays interest annually. Using the calculated duration estimate the approximate change in the bond price if the market interest rate increases to 4.50%. Explain how the duration of a bond is affected by the coupon rate. What does this relationship tell you about the important link between a bond's coupon and its interest rate sensitivity