Find the surface area of a sphere of radius $7 \, cm$. (in $, cm^{2}$)

Diameter of the base of a cone is $10.5\, cm$ and its slant height is $10\, cm$. Find its curved surface area. Assume $\pi = \frac{22}{7}$. (in $, cm^2$)

Find $(i)$ the curved surface area and $(ii)$ the total surface area of a hemisphere of radius $21\, cm$.

$A$ child is playing with building blocks, which are in the shape of cubes, and has built a structure as shown in the figure. If the edge of each cube is $3 \, cm$, find the volume of the structure built by the child. (in $cm^3$)

$A$ cubical box has each edge $10\, cm$ and another cuboidal box is $12.5\, cm$ long,$10\, cm$ wide and $8\, cm$ high. Which box has the greater lateral surface area and by how much (in $, cm^2$)?

The inner diameter of a cylindrical wooden pipe is $24 \, cm$ and its outer diameter is $28 \, cm$. The length of the pipe is $35 \, cm$. Find the mass of the pipe,if $1 \, cm^3$ of wood has a mass of $0.6 \, g$. (in $, kg$)