Curved surface area of a hemisphere $= \ldots \ldots \ldots$

Find the surface area of a sphere with a diameter of $3.5 \, cm$. Assume $\pi = \frac{22}{7}$. (in $, cm^2$)

The radius of a sphere is $3.5\, cm$. Find the cost of plating gold on its surface at the rate of ₹ $150$ per $cm^{2}$. (in ₹)

The radius of a sphere is decreased by $20 \% .$ By what per cent does its curved surface area decrease (in $\%$)?

The radii of three out of four spheres are $33 \, cm$,$44 \, cm$,and $48 \, cm$ respectively. If the surface area of the fourth sphere is equal to the sum of the surface areas of the first three spheres,find the radius of the fourth sphere (in $cm$).

The radius of a spherical balloon increases from $7 \, cm$ to $14 \, cm$ as air is being pumped into it. Find the ratio of surface areas of the balloon in the two cases.