Question

This math question i really dont get..

A city park contains a cylindrical artificial pond that has a radius of 7.5 m. A 2 m concrete deck will be constructed around the pond. The concrete should be at least 15 cm thick. Calculate the minimum volume of concrete required to construct the deck, to one decimal place. Draw a diagram.

Answer 1

diagram below

ok so what you do is find area of total-areapond=areaaround
then times that by the height

areatotal=pir^2
r=7.5+2=9.5
aeratotal=pi9.5^2=90.25pi

areapond=pi7.5^2=56.25pi

areaaround=90.25pi-56.25pi=34pi

volume=area times height
34pi m^2
15 cm thick
convert 15cm to m
0.15m
34pi times 0.15=5.1pim^3=16.02m^3

volume=16.0 m^3
if converted to cm
v=16022122.5 cm^3