How many right angles are in a regular pentagon?

If you are interested, it is easy to prove that regular $N$-sided polygon has each interior angle equal to
$\phi = {180}^{o} \cdot \frac{N - 2}{N}$ (degrees.)
So in case of a regular $5$-sided polygon (pentagon) the interior angles measure at
$\phi = {180}^{o} \cdot \frac{5 - 2}{5} = {108}^{o}$