Find the indicated partial derivatives $(2$ points each$).$

$($a$)\frac{de{l}^2}{\text{d}\text{e}\text{l}\text{x}\text{d}\text{e}\text{l}\text{y}}(4xy{e}^{-x^{2}y})$

$($b$)\frac{de{l}^2}{del{y}^2}(ln(5-x^2{y}^2))$

$($c$)\frac{de{l}^2}{\text{d}\text{e}\text{l}\text{x}\text{d}\text{e}\text{l}\text{y}}(cos(4x{y}^2))$