I'm sorry, but I don't understand what this means...?

To solve for A, B, C, and D, try picking x-values that make your life easier. In this case, an obvious choice would be x = 4, giving you:

16 - 116 + 5 = 0 + B(16 + 3) + 0

-95 = 19(B)

-5 = B

There are no other x-values which will zero out any of the factors, but you can pick some other "nice" values, such as x = 0:

5 = A(-4)(3) - 5(3) + (D)(16)

5 = -12A - 15 + 16D

20 = -12A + 16D

Pick a couple other values, and thus obtain a system of three equations in three unknowns. Solve the system for A, C, and D.