You can put this solution on YOUR website! This is saying it wants you to find out what F(x) would be if x were -3.
So you would plug in -3 where x is
.
f(x) = 4x - 6
f(x) = 4(-3) - 6 ----- then solve
f(x) = -12 - 6
f(x) = -18
.
So then f(-3) = 18
If you need me to explain it a different way then just tell me.