Write down the Euler's formula and verify it for the following.

Pentagonal prism

Write down the Euler's formula and verify it for each of the following.

Hexagonal prism

Write down the Euler's formula and verify it for the following.

Cuboid

Write down the Euler's formula and verify it for the following.

Triangular pyramid

Write down the Euler's formula and verify it for the following.

Rectangular pyramid

Write down the Euler's formula and verify it for the following.

Pentagonal pyramid

Write down the Euler's formula and verify the following.

Hexagonal pyramid

Write down the Euler's formula and verify the following.

Regular octahedron

If a polyhedron has $30$ edges and $20$ vertices, how many faces does it have?