Surface area of a cuboid = $\ldots \ldots \ldots$

Lateral surface area of a cube $= \ldots \ldots \ldots$

Write True or False and justify your answer in each of the following:
If the radius of a cylinder is doubled and its curved surface area is not changed,the height must be halved.

The surface area of a sphere is $7850 \, cm^2$. Find its radius in $cm$. (Use $\pi = 3.14$)

State whether the following statement is true or false:
The ratio of the surface areas of two spheres is $81: 49$. Then,the ratio of their volumes is $729: 343$.

Find the curved surface area and the total surface area of a hemisphere with a diameter of $14 \, cm$.