Answer :

AL2006

                                        5x³  +  30x²  +  15x

Take out a common factor of  5x :    5x (x² + 6x + 3)

The factors of the quadratic portion are  [ x - (-3 + √6) ] and [ x - (-3 - √6) ].

So finally, we wind up with:

                                     5x (x + 3 - √6) (x + 3 + √6) .