(x+3)(x-3) results in a product which is the difference of two squares: x^2 - 3^2.
Multiply this (x^2 - 3^2) by the third factor, (3x+2):
3x^3 - 9x + 2x^2 - 3^2*2, or, in descending order by powers of x,
3x^3 + 2x^2 - 9x - 18
