Find the surface area of a sphere with a diameter of $21\, cm$ (in $cm^2$).

$A$ well,$20 \, m$ deep,is $7 \, m$ in radius. Find the cost of cementing the inner curved surface at the rate of ₹ $15$ per $m^2$. (in ₹)

State whether the following statement is True or False and justify your answer: In a right circular cone,the height,radius,and slant height do not always form the sides of a right triangle.

$1 \, m^{2} = \ldots \ldots \, cm^{2}$

The edge of a cube is $35\, cm$. Find the total surface area of the cube (in $cm^2$).

The curved surface area of a cylinder is $8800 \, cm^2$. If the radius of the cylinder is $28 \, cm$,find its volume in $cm^3$.