f(x) = [3-x]?

there has to be more to this question. This is just a statement without anything to solve. Are you given a value for x? If so, then substitute that value and solve for f(x). f(x) is simply notation for “y”. So your “question” is stating that y=3-x. More information is needed.

Is this the whole problem …. doesnt look like it, because you are saying that F of X is equal to “3-X” but thats just an equation, is there a problem where you are suppose to plug

F(x) into?

The answer is 42