Please see link below to Khan Academy - Area between curves
https://www.khanacademy.org/math/ap-calculus-ab/ab-applications-of-integration-new/ab-8-4/v/area-between-curves
Area between curves example - Khan Academy
https://www.khanacademy.org/math/ap-calculus-ab/ab-applications-of-integration-new/ab-8-4/v/area-between-curves-example
Area between curves and the y-axis - Khan Academy
https://www.khanacademy.org/math/ap-calculus-ab/ab-applications-of-integration-new/ab-8-5/v/area-between-two-functions-of-y
Horoizontal area between curves (using y coordintes) - Khan Acaademy