Introduce your young math scholars to functions. Because the answer is explained at the bottom of the page, consider projecting this and covering it up until you hear the class responses. They observe a rule (in this case to add 15) and complete a table with six numbers in the first column, labeled in. The second column, out, has one example and the rest blank for learners to complete. They add 15 to all the first numbers to finish the problem. Explain it as a "math machine" that takes in numbers, changes them, and spits them back out!