18. The inner diameter of a circular well is 3.5m. It is 10m deep. Find: (a) its inner curved surface area (b) the cost of plastering its curved surface area at the rate of Rs 40 per sq m.
19. A conical tent is 10m high and radius of its base is 24m. Find: (a) Slant height of the tent. (b) Cost of the canvas required to make the tent, if the cost of 1 sq m canvas is Rs 70.
20.Find the radius of a sphere whose surface area is 154 sq cm.
21. A godown measure 40m x 25m x 15m. Find the maximum number of wooden crates each measuring 1.5m x 1.25m x 0.5m that can be stored in the godown.

plz solve it