How do you evaluate a function?

substitute the input (the given number or expression) for the function's variable (place holder, x). Replace the x with the number or expression.

Example:

f (x) = 3x-5 and f (4)

f (x) = 3 (4) - 5

f (x) = 12-5

f (x) = 7

final answer is (4,7)