Two investments, $x$ and $Y,$ have the characteristics shown below.

$E(x)=$$$70,E(Y)=$$$100,{}_x^2=7,000,{}_Y^2=16,000,$ and ${}_{xY}=7,500$

If the weight of portfolio assets assigned to investment $x$ is $0\mathrm{.}4,$ compute the

a$.$ portfolio expected return and

b$.$ portfolio risk.