Explanation:
Changes made to your input should not affect the solution:
(1): "x3" was replaced by "x^3". 2 more similar replacement(s).
((3•(x2))+(9•(x2)))-3x3
((3 • (x2)) + 32x2) - 3x3
(3x2 + 32x2) - 3x3
Pull out like factors :
12x2 - 3x3 = -3x2 • (x - 4)
-3x^2 • (x - 4)