How to solve this calculus problem This question was on my quiz for Calc AB, everyone was confused on how to solve it and I did some random substitution but was still getting nowhere. My teacher said it's possible to do it but not possible with the knowledge we have currently and she's going to throw out the problem. The problem was as following:

$$\frac{\mathrm{d}y}{\mathrm{d}x}=y-3x$$


Multiply by $e^{-x}$:
$$y'e^{-x}-ye^{-x}=-3xe^{-x}$$
Integrating we obtain: $$ye^{-x}=3(x+1)e^{-x}+C$$
$$y=3x+3+Ce^{-x}$$
