Five years ago, Rock Steady Corp issued a semiannual coupon bond with seven years until maturity. This bond was originally issued at par with a $1,000 face value.

The coupon rate on the bond is 8%. Today, the yield-to-maturity (YTM) is 10%.

What was yield to maturity of this bond when it was issued?

a) 9%

b) 7.5%

c) 8.5%

d) 8%

please show how!!