y=18.
All triangles are 180 degrees. The given angle is 108 degrees. 180 - 108 = 72. 72 degrees are left to solve for in the triangle. 72 degrees / the two angles = 36. The angles of the triangle are 108, 36, 36. The 36 degree angle = 2y. 36 / 2 = 18.
Y=18
