"-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.
