The surface area of the cylindrical drum of radius 21cm, height 50cm open at the top.
radius R = 42 cm
length L = 220.5 cm
bottom surface SB = 3.14 x R x R = 3.14 x 42 x 42 = 5539 square cm
top surface ST = 3.14 x R x R = 3.14 x 42 x 42 = 5539 square cm
bottom circumference BS = 3.14 x 2 x R = 3.14 x 2 x 42 = 264 cm
wall surface area WS = BS x L = 264 x 220.5 = 58212 square cm
whole outside surface area SB + ST + WS = 5539 + 5539 + 58212 = 69290 square cm
whole inside and outside surface area 69290 + 69290 = 138,590 square cm
the cost of painting the drum's inside and outside walls Rs. 0.15 x 138,590 = Rs20787
