From the diagram, 6y = 90 [right angle]
y = 90/6 = 15
Also, 5y + 3x + 6y + 90 = 360 [sum of interior angle of a quadrilateral is 360]
5(15) + 3x + 6(15) + 90 = 360
75 + 3x + 90 + 90 = 360
3x = 360 - 255 = 105
x = 105/3 = 35
Therefore, x + y = 35 + 15 = 50.