Find ∫ (e^3x)-(x^2)/(e^3x)-(x^3)

Hi I'm meant to use the rule f'(x)/f(x)

However I can't quite figure out how to do this. The answer sheet says f'(x)/f(x) ends up as 1/3 ∫(3e^3x) -(3x^2) / (e^3x) - (x^3) but I cant figure out how they get to this point