Answer:
D is 12
Step-by-step explanation:
75 - 63 = 12 = D
For f(3)...put 3 as the value of x in f(x)
for x.....put the value of f(x) from the given and equate it with 14..and solve
We can write out a formula in order to solve this. Since sum represents addition, if x represents the unknown number, we can write the formula: x+51=-21. Then, to solve for x, you would subtract 51 from both sides to get x=-72 which is the final answer.
The answer to your question is 20