MAT 161 Reading and Video

Section 4.5 Related Rates.
Video:
https://www.khanacademy.org/math/calculus/derivative_applications/rates_of_change/v/rates-of-change-between-radius-and-area-of-circle

https://www.khanacademy.org/math/calculus/derivative_applications/rates_of_change/v/rate-of-change-of-balloon-height