I have read the theory but I don't understand how to use is.

Don't know where to put the 2 before y'' when I'm solving and can't really solve it. If you have an hyperlink with more explanations and examples of solutions of ODE's I would also appreciate it.

Thanks!

$\displaystyle 2y''+3y'+y=x^{2}+3\sin x , y(0)=12.5 , y'(0)=-6$