Raees has identified a risky portfolio which has an expected return of $13\%$ and a standard deviation of $8\%.$ The optimal investment in the risky portfolio for Raees is $150\%.$ The risk$-$ free rate is $0\mathrm{.}6\%.$

$($a$)$ What is the reward$-$to$-$risk ratio of the optimal complete portfolio? $(3$ marks$)($b$)$ If the risk$-$free borrowing rate is $0\mathrm{.}8\%$ higher than the risk$-$free lending rate, what is

the new reward$-$to$-$risk ratio of this portfolio?