b$)$ Use master's method to compute the asymptotic complexity for the following recurrences. In each case, identify the case of master method that it uses to compute the asymptotic complexity. $(5-$Marks$)$

$($a$)T(n)=16T(\frac{n}{4})+n^2$

$($b$)T(n)=3T(\frac{n}{3})+n^{\frac{1}{2}}$