When the quadrilateral is inscribed in a circle, opposite angles add to 180°.
26y +2x = 180
21y +3x = 180
There are many ways to solve these equations. Shown here is a graphical solution that tells us
x = 25
y = 5
Then the angles are ...
∠A = 26y° = 130°
∠B = 3x° = 75°
∠C = 2x° = 50°
∠D = 21y° = 105°
