The sum of interior angles of a trapezoid is 360°.
The pair of bottom angles are equal, also the pair of top angles.
So:
(4x) + 4x + (6x+20) + (6x+20) = 360
Solve for x:
4x + 4x +6x +20 +6x + 20 = 360
Combine like terms:
4x+4x+6x+6x +20+20 =360
20 x + 40 = 360
20x = 360-40
20x = 320
x = 320/20
x = 16
Replace x on (6x+20)
6(16)+20 = 116°
y= 116°