A swimming pool 12 $m$ long, 8 $m$ wide and 2 $m$ deep is to be tiled on its floor and on its four walls at ₹90 per $m^2$. Find the total cost in rupees.

Floor = $12\times 8=96{\text{m}}^2$. Walls = $2(12+8)\times 2=80m^2$. Tiled area = $176{\text{m}}^2$, so the cost = $176\times 90$ = ₹15840. (₹8640 tiles the floor only and ₹7200 the walls only; adding a $96{\text{m}}^2$ 'ceiling' as though the pool were a closed box gives ₹24480, but a pool is open at the top.)