Okay, so as you know, the question starts off as this:
9x^3 + 2x^2 -5x +4 -(5x^3 -7x +4)
Distribute the negative:
9x^3 + 2x^2 -5x +4 -5x^3 +7x -4
Combine like terms:
9x^3 -5x^3 +2x^2 -5x +7x +4 -4
4x^3 +2x^2 +2x
You can either end it there or
Divide by x:
4x^2 +2x +2
