$CSA$ of a cylindrical tank with diameter $2.1 \, m$ and height $5 \, m$ is $\ldots \ldots \ldots \ldots \, m^2$.

Write 'True' or 'False' and justify your answer:
Two identical solid hemispheres of equal base radius $r \text{ cm}$ are joined together along their bases. The total surface area of the resulting solid is $6 \pi r^{2}$.

The volume of a sphere with radius $1.5 \text{ cm}$ is $\ldots \ldots \ldots \text{ cm}^3$.

From a solid cube of side $7 \, cm$,a conical cavity of height $7 \, cm$ and radius $3 \, cm$ is hollowed out. Find the volume of the remaining solid (in $cm^3$).

Volume of a hemisphere $= \ldots \ldots$

The surface area of a sphere with radius $7\,cm$ is $\ldots \ldots \ldots \ldots cm ^{2}$.