v=(4/3)pir^2
4. r=7 ft so v=(4/3) x 3.14 x 7^2 = 205.1 ft.^3
5. r=18/2 = 9 so v=(4/3) x 3.14 x 9^2 = 339.0 mm^3
7. r = 3, so v=(4/3) x 3.14 x 3^2 = 37.7 cm^3
