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.

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