Answer:
Step-by-step explanation:
Given that f(x) = 3x + 21
Plug in 3 for x
F(3)= 3(3) +21
F(3) = 9+21
f(3) = 30
Plug in 7 for x
F(7)= 3(7) +21
F(7) = 21+21
f(7) = 42
