Find general solutions of the following differential equations:

$($a$)$

$\frac{d^{2}y}{d{x}^2}+6\frac{dy}{dx}+9y=5sinx$

$($b$)$

$\frac{d^{2}y}{d{x}^2}-4\frac{dy}{dx}+12y=4e^{-2x}$