Consider a bond with a 5.7% coupon and a yield to maturity of 9.3% maturing in just over 18 years. Suppose the bond was purchased 107 days after the most recent coupon was paid. If there are 180 days in the current coupon period, find (based on $1000 face value)

(b) The Clean Price

The answer is 686.741770.01, but I don't know how to calculate, please explain.

My answer is 686.898 which is very close but it's marked as incorrect.