y=125
the angle adjacent to 135 is 45 degrees and the angle adjacent to 100 is 80 degrees. when you add 45 + 80 you get 125. then you would subtract 180-125 (which equals 55) to get the angle that is adjacent to y. then you take 180-55 to get y. or you can remember that all the angles outside of the triangle add up to 360 and just subtract 360-100-135 which equals 125.
