In order to not get confused, start by converting cm to m h=20 cm = 0.2m and r=5cm = 0.05m
The cans are cylinders and we only need the rectangular shape, which is equal to the height x the circumference of the circle (2r(pi)), which you'll have to multiply by 200,000 for the number of cans necessary
your equation is therefore: A=200,000h(2pi(r)) A=200,000(0.2)(2)(0.05)(pi) A=4000pi m^2