It's almost impossible to give a reasonable answer because you have given no indication of what you know about the problem, or what hints would help. I would recommend looking for integer or rational roots, using the "rational root theorem". Do you know what that is? If you can find two rational roots, you can then use synthetic division to reduce to a quadratic function of the remaining roots and, perhaps, use the quadratic formula to solve that.

Do you know what "synthetic division" is? If not you should first look it up in your text book or "google" "synthetic division".