The sum of the polynomials is -11x - 3y^2.
In order to find this we must first collect all like terms. To start, we'll begin with all x^2 terms.
8x^2 - 9x^2 + x^2 = 0
Since these all cancel, we're left with no x^2 term. Next we'll do x terms.
-4x - 7x = -11x
The only thing left is -3y^2, which has no alike term. so we just include that in there.
-11x - 3y^2
