Answer:
3 - x
Step-by-step explanation:
f(x) = -x + 6
f(x + 3)
Substitute (x + 3) in for x;
f(x + 3) = -(x + 3) + 6
= - x - 3 + 6
= -x + 3
-3x+10=21
-3x=21-10
-3x=11
x=11/-3
x=- 11/3
I hope that it helps you..
the answer is C
