Answer:
Step-by-step explanation:
Combine like terms:
-4x - 9x = (-4 - 9)x = -13x
4x - (-9x) = 4x + 9x = (4 + 9)x = 13x
-4x + 9x = (-4 + 9)x = 5x
4x - 9x = (4 - 9)x = -5x
