the answer is
f(x) = 9x3 + 18 x2 - 135x can be written as f(x) = x( 9x2+ 18 x - 135)
the first zero must be = 0
let's find the another zeros by solving 9x2+ 18 x - 135=0
f(-5)=135-135=0, so the answer is
0, -5, and 3
because f(x) = 9x3 + 18 x2 - 135x =x (x+5)(x-3)
