Stock A has an expected return of $18\%$ and a standard deviation of $31\%.$ Stock B has an expected return of $13\%$ and a standard deviation of $15\%.$ The risk$-$free rate is $6\mathrm{.}4\%$ and the correlation between Stock A and Stock B is $0\mathrm{.}3.$ Build the optimal risky portfolio of Stock A and Stock B$.$ What is the expected return on this portfolio?