first try the factors of 3 into the formula to see if we can get zero. we realize that plugging in gives zero. thus is a root of the cubic, and so is a factor, by the factor theorem.
by way of polynomial long division or synthetic division, we find that:
and you can continue to factor the quadratic, but only if you really want to, it will be tedious to work out, and it won't look very nice when you're done, if you decide to