Total surface area of a cone is $616 \mathrm{sq}. \mathrm{cm}$. If the slant height of the cone is three times the radius of its base, find its slant height.

The inner diameter of a well is $4.20$ metre and its depth is $10$ metre. Find the inner surface area of the well. Find the cost of plastering it from inside at the rate of $₹52$ per square metre..

The length of a road roller is $2.1 \mathrm{m}$ and its diameter is $1.4 \mathrm{m}$. For levelling ground $500$ rotations of the road roller were required. How much area of ground was levelled by the road roller? Find the cost of levelling at the rate of $₹7$ per square metre.