In this tutorial, we learn how to evaluate functions. A function is an equation with an input and an output. For the value of "X" there is going to be a value for the rest of the values that are in the equation. To start, write out the equation, then substitute the "x" with the appropriate number. After this, substitute the "x" in the rest of the equation where it belongs. Once finished, work out the rest of the equation in the appropriate order. Now you will be able to finish it and get the correct number. Do this for all equations, then do backwards to make sure your answer is correct.