What is the sum of the polynomials? (8x2-9y2-4x)+(x2-3y2-7x)

The sum of the polynomials (8x²-9y²-4x)+(x²-3y²-7x) is:

 1. You must add the terms whose variables and exponents are the same. 
 2. Let's rewrite the polynomials:

 (8x²-9y²-4x)+(x²-3y²-7x)
 8x²-9y²-4x+x²-3y²-7x
 (8+1)x²+(-4-7)x+(-9-3)y²

 3. Therefore, the result is:

 9x²-11x-12y²

 3. What is the sum of the polynomials?

 The answer is: 9x²-11x-12y²

I'm just guessing, but my answer would c. 0 to 300.