Solve $11-15$:

$11.y^{\text{'}\text{'}}+y^{\text{'}}-2y=2t,y(0)=0,y^{\text{'}}(0)=1$

$12.y^{\text{'}\text{'}}+4y=t^2+3e^t,y(0)=0,y^{\text{'}}(0)=2$

$13.y^{\text{'}\text{'}}-2y^{\text{'}}+y=t{e}^t+4,y(0)=1,y^{\text{'}}(0)=1$

$14.y^{\text{'}\text{'}}+4y=3sin(2t),y(0)=2,y^{\text{'}}(0)=-1$

$15.y^{\text{'}\text{'}}+2y^{\text{'}}+5y=4e^{-t}cos(2t),y(0)=1,y^{\text{'}}(0)=0$