A stock has an expected return of $13$ percent and a beta of $\mathrm{.}8,$ and the expected return on the market is $15$ percent. What must the risk$-$free rate be$?$

$7\mathrm{.}0\%$

$8\mathrm{.}0\%$

$5\mathrm{.}0\%$

$6\mathrm{.}0\%$