The sum of pairs of co-interior angles on the same sides of the transversal is [[1]]

We know that the sum of pairs of co-interior angles on the same sides of the transversal is 180°.

For example:

From the figure, angles b and angle e are pairs of co-interior angles on the same sides of the transversal p.
So, $\angle \mathrm{b} + \angle \mathrm{e} = 180°$