First of all find the surface area of the given hemisphere by relating the cost to the rate .

Find the volume of the water inside the cylidrical vessel and then find the volume of spherical ball .

Find the internal volume of the spherical tank and subtract this volume from the external volume of the spherical tank.

Put the values in the formula and do the calculations correctly .

Try to find the radius of the sphere and then find the volume of sphere .

Compare the initial and new volume to find the ratio.

Find the internal volume of the spherical tank and subtract this volume from the external volume of the spherical tank.

According to the question you should first find the CSA with original radius then decrease the radius by 50% and find the reduced CSA.

Put the values in the formula and do the calculations correctly .

Put the values in the formula and do the calculations correctly .