You can only cut down a integer number of trees. So you might look at a few integer values for x. As x get large the –x4 term dominates the expression for big losses. x = 0 is easy P(x) = -6. Without cutting any trees you have lost money Put x = 1 and you get for the terms in order -1 + 1 + 7 -1 -6 = 0. So P(x) crosses zero just before you cut the first tree. So you make a profit on only 1 tree. However when x=10 you are back into no profit. So compute a few values for x = 1,2,3,4,5,6,7,8,9.
