(x - 2)(x + 3) = x^2 + x - 6
(x - 4)(2x + 5) = 2x^2 -3x -20
(x^2 + x - 6) - (2x^2 -3x -20)
x^2 + x - 6 - 2x^2 +3x + 20 = -x^2 + 4x +14
If 0 = -x^2 + 4x +14, then this may be solved with the quadratic equation. However, you did not indicate that it is an equation, only an expression. Therefore it may only be simplified.