The answer is a. x^7 + x^6 + 2x^5 -2x^4 - 5x^3 -x^2 +17x +17
As a rule for addition / subtractionof exponents you can only add variables with the same exponential degree and base. Say for example,
You can add 2x² +3x², result is 5x² or subtract 2x² - 3x², result is -1x²
But you cannot add 2x² + 3x³, the result is 2x² + 3x³. They have different exponential degree.
