Do you multiply or divide calories?

If f(x) = 2x + 8 and g(x) = x4, what is (gº)?

You are standing next to a really big circular lake. you want to measure the diameter of the lake, but you don't want to have to swim across with a measuring tape! you decide to walk around the perimeter of the lake and measure its circumference, and find that it's 400\pi\text{ m}400? m. what is the diameter dd of the lake?

Asequence is a function whose is the set of natural numbers