let's bear in mind that, the sum of all interior angles in a polygon is
180(n - 2), n = number of sides in the polygon.
now, this is a PENTAgon, it has 5 sides, thus n = 5, so the sum of all interior angles is then, 180( 5 - 2) => 180(3) => 540°.
now let's add them up then.
