Length of the tank = 30 m
Width of the tank = 24 m
Depth of the tank = 4.5 m
Area of four walls of the tank = 2[L+B] x H = 2(30 + 24) x 4.5 = 2 x 54 x 4.5 m2
Area of the floor of the tank = L x B = 30 x 24 = 720 m2
Area of Iron sheet required to make the tank = Area of four walls + Area of floor = 486 + 720 = 1206 m2
Cost 2 of iron sheet required @ Rs. 65 per m = 1206 x 65 = Rs. 78390