A 15 year bond has a par-value of 500 and pays semi-annual coupons at a 7% rate. An investor purchases the bond at a price such that its yield to maturity is 6% convertible semi-annually. The investor sells the bond immediately after 8th payment at a price such that its new owner's yield to maturity is 5% convertible semi-annually. What was the original investor's yield convertible semi-annually on this investment over the 4-year period?