$7.($YTM$,$ semiannual payments$)$ On $15$ August $1990,$ the U$.$S$.$ Treasury issued a bond maturing on $15$ February $2020.$ The bond has a coupon rate of $8\mathrm{.}75\%,$ payable semi$-$annually on $15$ February and $15$ August. If on $22$ June $2015$ a $$100$ face value bond is selling for $$138\mathrm{.}89,$ what is the bond's yield to maturity