Question

Find f(-3) for f(x) = 3x - x²
A. f(-3) = 18
B. f(-3) = -15
C. f(-3) = 0
D. f(-3) = -18

Answer 1

if I had x+2=5
and I said that 5-2=x so 3=x
then I said that
f(x)=x+2
and find f(3)
then you see from f(x) we have a function of x (the stuff in the brackets)
and for f(3) we have a function of 3

so basically, let x=3
if I had f(4) let x=4

so in your case, f(-3), let x=-3, substitute it into the function, and that is your answer

Answer 2

that is, f(-3)=3(-3) - (-3)^2