Question

3x²y²dx + 4(x³y -3) dy = 0

Answer 1

$3x^2y^2dx+4(x^3y-3)dy=0$

integrating factor is $y^2:$

$3x^2y^4dx+4x^3y^3dy-12y^2dy=0$

The left part is the full differential of the next function:

$x^3y^4-4y^3=C$