Since the two lines with red arrows are parallel, that means the two angles on the left are both 90º angles.
2x = 90
or x = 45
Now, 2x + 90 + y + (y-50) = 360, since this is a quadrilateral and we know 2x=90.
So 90 + 90 + y + y-50 = 360
or 2y + 130 = 360
or 2y = 230
or y = 115
To check, add up the angles to make sure it adds to 360:
90 + 90 + 115 + 65 = 360.