Solve the given initial$-$value problem.

$\frac{dy}{dx}+P(x)y=e^x,y(0)=-4,$ where

$P(x)=\{\begin{array}{cc}1,& 0x<mn>1</mn>\end{array}$

$-1,x1$

$y(x)=\{\begin{array}{cc},& 0x<mn>1</mn>\end{array}$

$,$