$A$ cylinder is closed at both the ends by hemispheres. The radius of the cylinder is $7 \, cm$ and the total height of the article is $34 \, cm$. Find the total surface area of the article. (in $cm^2$)

The volume of a cylinder is $550 \, cm^{3}$ and its radius is $5 \, cm$. Then,the height of the cylinder is $\ldots \ldots \ldots \, cm$.

$A$ cylinder with radius $8 \, cm$ and height $9 \, cm$ is surmounted by a cone of height $15 \, cm$. Find the total surface area and the volume of the combined solid.

If the radius of a sphere is doubled,its volume becomes $\ldots \ldots \ldots \ldots$ times the original volume.

Write 'True' or 'False' and justify your answer:
The curved surface area of a frustum of a cone is $\pi l(r_{1}+r_{2})$,where $l = \sqrt{h^{2}+(r_{1}+r_{2})^{2}}$,$r_{1}$ and $r_{2}$ are the radii of the two ends of the frustum,and $h$ is the vertical height.

The volume of a cone with radius $5 \, cm$ and height $21 \, cm$ is $\ldots \ldots \ldots \, cm^{3}$.