Y '+ y = 3x for general solution of differential equation

Y '+ y = 3x for general solution of differential equation

y'+y=3x
Let 3x-y = U
dy=d3x-du
dy/dx+y=3x
3-du/dx=u
du/(3-u)=dx
ln|u-3|=-x+C0
u-3=Ce^(-x)
u=Ce^(-x)+3
The general solution y = 3x CE ^ (- x) - 3