Factor - 4d 3 + 28d 2 - 4d. - 4d (d2 - 7d + 1) - 4 (d2 - 7d + 1) - 4 (d3 - 7d2 + 1)

"-4d 3 + 28d 2 - 4d" might mean more to you as well as to others if typed as

-4d^3 + 28d^2 - 4d. The " ^ " symbol calls for exponentiation, whereas d 3 is meaningless.

Have a close look at - 4d^3 + 28d^2 - 4d. Notice that - 4d is a factor of every term? Thus, - 4d^3 + 28d^2 - 4d = - 4d (d^2 - 7d + 1. Now all we have to do is factor d^2 - 7d + 1

Actually, the factors - 4d and d^2 - 7d + 1 are all we need, and the first answer is the correct one.

An important skill here is identifying common factors in a series of terms.