Solve the following boundary value problems using Separation of Variables.

$($a$)x^2+y^2\frac{dy}{dx}=0,y=3$ when $x=0$

$($b$)1+e^{x}cosy\frac{dy}{dx}=0,y(0)=\frac{}{3}$

$($c$)y\frac{dy}{dx}=x{y}^2+4x,y(0)=0$