$ay(0)=0$ and $y^{\text{'}}(0)=0.$

$i.\frac{d^{2}y}{d{t}^2}+5\frac{dy}{dt}+6y=12$

$ii.y^{\text{'}\text{'}}-6y^{\text{'}}+9y=e^{3x}{x}^2$

$b3u(t-2)-2u(t-4)$