A) 7x^3 + 13x^2 + 8x + 9
Step-by-step explanation:
(3x^2 + 2x + 7x^3) + (10x^2 + 6x + 9)
I like to line them up vertically
7x^3 +3x^2 + 2x
+ (10x^2 + 6x + 9)
7x^3 +13x^2 +8x +9