so hmm notice the picture below
so all internal angles then, are "a", "a", 90, 113, and 105
now the sum of all internal angles of a regular polygon, is 180( n - 2), where n = number of sides in the polygon
well, this is a PENTAgon, or PENTA=5, 5 sides, so, it has a total of
180( 5 - 2) internal angles or 540
thus

since, angle "y" is sitting on a flat-line with angle "a", then, y = 180 - a
and, sure you know how much that is