$CSA$ of a hemisphere with diameter $20 \, cm$ is $\ldots \ldots \ldots cm^{2}$. (in $\pi$)

The $CSA$ of a cone with radius $7\, cm$ and slant height $15\, cm$ is $\ldots \ldots \ldots \, cm^2$.

Write 'True' or 'False' and justify your answer:
$A$ solid cylinder of radius $r$ and height $h$ is placed over another cylinder of the same height and radius. The total surface area of the shape so formed is $4 \pi r h + 4 \pi r^2$.

$A$ fez,the cap used by the Turks,is shaped like the frustum of a cone (see $Fig.$). If its radius on the open side is $10 \, cm$,radius at the upper base is $4 \, cm$ and its slant height is $15 \, cm$,find the area of material used for making it.

Derive the formula for the curved surface area and total surface area of the frustum of a cone.

The $TSA$ (Total Surface Area) of a hemisphere is equal to $\ldots \ldots \ldots$