For each of the following
(i) draw the two indicated curves on the provided axes,
(ii) draw a representative Riemann rectangle that will be useful for finding the area bounded between the two curves, and
(iii) calculate that bounded area.

article:What is Pi? - Live Science

"Pi r squared. In basic mathematics, pi is used to find the area and circumference of a circle. Pi is used to find area by multiplying the radius squared times pi. ... Because circles are naturally occurring in nature, and are often used in other mathematical equations, pi is all around us and is constantly being used"

edited

"circumference of a circle is 20 centimeters and you want to calculate the radius. Just plug the value for the circumference into the equation and solve. Remember that pi is approximately equal to 3.14."

source: https://www.livescience.com/29197-what-is-pi.html