Verify the Euler's formula for the following Cube

Draw the net of a cube and fill the places with the numbers $3, 4, 5, 6, 7, 8$, such that sum of the opposite faces becomes $11$.

When a cube is represented in 2-D, how many faces are shown as hidden faces?

Two cones of equal shape and height are placed together such that one of them is vertically opposite , i.e., upside down. What shape does this combination form?

What shape will you get, if you place three cubes each of side $2 \mathrm{cm}$ together in the same place? Write the dimensions also.

The two dimensions of the box are $4 \mathrm{m}$ and $3 \mathrm{m}$. Compute the third dimension of the box so that the space diagonal of the box is an integer.

How many faces does a stellated dodecahedron have?