$A$ toy is in the form of a cone of radius $3.5 \, cm$ mounted on a hemisphere of the same radius. The total height of the toy is $15.5 \, cm$. Find the total surface area of the toy (in $cm^2$). $\left[ \text{Use } \pi = \frac{22}{7} \right]$

The decorative block shown in the figure is made of two solids - a cube and a hemisphere. The base of the block is a cube with edge $5 \, cm$,and the hemisphere fixed on the top has a diameter of $4.2 \, cm$. Find the total surface area of the block. (in $cm^2$) (Take $\pi = \frac{22}{7}$)

In one fortnight of a given month,there was a rainfall of $10 \, cm$ in a river valley. If the area of the valley is $7280 \, km^2$,show that the total rainfall was approximately equivalent to the addition to the normal water of three rivers each $1072 \, km$ long,$75 \, m$ wide,and $3 \, m$ deep.

$A$ solid consisting of a right circular cone of height $120\, cm$ and radius $60\, cm$ standing on a hemisphere of radius $60\, cm$ is placed upright in a right circular cylinder full of water such that it touches the bottom. Find the volume of water left in the cylinder,if the radius of the cylinder is $60\, cm$ and its height is $180\, cm$. [Take $\pi = \frac{22}{7}$.] (in $m^3$)

From a solid cylinder whose height is $2.4 \, cm$ and diameter is $1.4 \, cm$,a conical cavity of the same height and same diameter is hollowed out. Find the total surface area of the remaining solid to the nearest $cm^2$. [Take $\pi = \frac{22}{7}$]

Derive the formula for the volume of the frustum of a cone.