i dont get this question 3x^3+9x^2+6x=3x(x+1)(?)?

take 3x common

3x(x^2+3x+2)

now x^2+3x+2 beign quadratic = (x+2)(x+1)

so expression = 3x(x+1)(x+2)

3x^3 + 9x^2 + 6x = 3x(x + 1)(?)
3x(x^2 + 3x + 2) = 3x(x + 1)(?)
3x(x^2 + 2x + x + 2) = 3x(x + 1)(?)
3x[(x^2 + 2x) + (x + 2)] = 3x(x + 1)(?)
3x[x(x + 2) + 1(x + 2)] = 3x(x + 1)(?)
3x(x + 1)(x + 2) = 3x(x + 1)(?)
? = x + 2

X=0,-1,-2

3x^3 + 9x^2 + 6x
= 3x(x^2 + 3x + 2)
= 3x(x + 1)(x + 2)

therefore...
(?) = (x + 2)

3x (x² + 3x + 2)
3x (x + 1) (x + 2)