How many cubic metres of the earth must be dug to construct a well $7 \mathrm{m}$ deep and of diameter $2.8 \mathrm{m}$? Write the answer in decimal in ${\mathrm{m}}^3$. [Take $\mathrm{\pi }=\frac{22}{7}$]

Radius of a cylinder is $\mathrm{r}$ and the height is $\mathrm{h}$. Find the change in the volume if the height is doubled.

Radius of a cylinder is $\mathrm{r}$ and the height is $\mathrm{h}$. Find the change in the volume if the height is doubled, and the radius is halved.

Radius of a cylinder is $\mathrm{r}$ and the height is $\mathrm{h}$. Find the change in the volume if the height remains the same, and the radius is halved.