Question

definition of F(x)?
and an example to help please
f(x)=-3x+2 x=3

Answer 1

Ok, f(x) means you are going to have a one-to-one function which means that if you plug a number like 3 then no matter what else you plug you will not get the same number.
f(x)=-3(3)+2 and solve
-7

Answer 2

So when a problem looks like yours it is basically saying this f of x equals some polynomial or number and when you have the second part (x=3) that is asking what is x when you plug in 3. Which can also be written like this when solving f(3)=-3(3)+2