The total surface area of a cube is $864 \, cm^2$. Then its edge is $\ldots \ldots \ldots \, cm$.

In a cylinder,if the radius is halved and the height is doubled,the volume will be

State whether the following statement is true or false:
The radius of a cone can be $3 \, cm$,slant height $4 \, cm$,and height $5 \, cm$.

Find the surface area of a sphere of diameter $3.5\,m$ (in $m^2$).

State whether the following statement is True or False and justify your answer:
$A$ cone,a hemisphere,and a cylinder stand on equal bases and have the same height. The ratio of their volumes is $1: 2: 3$.

The curved surface area of a cylinder is $550 \, cm^2$. If its height is $50 \, cm$,find its diameter in $cm$.