The surface area of a cylindrical drum of radius 21cm, height 50cm open at the top.
radius R = 21cm
height H = 50cm
bottom surface S = 3.14 x R x R = 3.14 x 21 x 21 = 1385 square cm
bottom circumference BS = 3.14 x 2 x R = 3.14 x 2 x 21 = 132 cm
wall surface area WS = BS x H = 132 x 50 = 6600 square cm
whole outside surface area S + WS = 1385 + 6600 = 7985 square cm
whole inside and outside surface area 2(S + WS) = 2(1385 + 6600) = 15970 square cm
