The calculus for for this section is simple. The integrand is always the function on top minus the function on the bottom. The hard part of these problems is determining which function is on top so you can set up your integral correctly. If you get a negative answer, it means you chose wrong. Additionally, if the graphs intersect then the function on top or bottom depends on the interval. See below for an example of an area that would require two different integrals to solve.