There is no general formula for solving polynomials of degree 5+ (and even the ones for degrees 3 and 4, the formulas are usually to complicated to implement efficiently), so often you look for tricky factorisations. You don't need it in this case.

Set to get a quadratic . Solve for , and then solve for .

For information about actual factorisations of higher degree polynomials, google 'factoring higher degree polynomials'. I took a look at the first few links and they all seem pretty good, so the choice is yours. Also this youtube video looks good for your case:Spoiler: