There's a couple of things you can do here. Do you know synthetic division?
You could use as your divisor and find P that way.
Perhaps an easier method would be to act like is a factor of in which case is a root. (Factor Theorem)
Now, set and find . (Remainder Theorem.) means when is substituted for x, the remainder is 0.
Once you've substituted for x, you'll can solve for p.