Answer:
= d^3 + d^2 + 12d + 18
Step-by-step explanation:
(d^2 + 6d + 9) + (d^3 + 6d + 9)
= d^2 + 6d + 9 + d^3 + 6d + 9
= d^3 + d^2 + 6d + 6d + 9 + 9
