The height of a right circular cylinder is $6 \, m$. $3$ times the sum of the areas of its two circular faces is equal to twice the area of its curved surface. The radius of the base is ...... $m$.

$A$ rectangular water tank is $80 \, m \times 40 \, m$. Water flows into it through a pipe with an opening area of $40 \, cm^2$ at a speed of $10 \, km/h$. By how much will the water level in the tank rise in half an hour (in $cm$)?

$A$ right prism has a triangular base whose sides are $13\, cm, 20\, cm$ and $21\, cm$. If the altitude of the prism is $9\, cm$,then its volume is......$cm^3$

The radius of a cylinder is doubled and the height is halved. What is the ratio between the new volume and the previous volume?

If a hemisphere is melted and four spheres of equal volume are made,the radius of each sphere will be equal to

The radius of a wheel is $3.5 \, cm$. What is the distance (in $cm$) travelled by the wheel in $20$ revolutions?