In the capital markets, we use duration as an approximate measure of a bond's price sensitivity to changes in interest rates. For simplicity, in this question, we define duration as the percentage change of the bond price if the market interest rate increases by 1%. Now please calculate the duration (the change in the bond's price if the YTM increases by 1%) of a bond which has a 7% coupon paid annually, maturing in 20 years. The bond's current YTM is 8%.