a) Angles 1 and 2 of this isosceles trapezoid are equal and supplementary to angles D and 3, which are also equal.
∠1 = ∠2 = 180° -55° = 125°
∠3 = ∠D = 55°
b) Top and bottom angles are equal.
(4x+15) = (5x-13)
28 = x . . . . . add 13-4x
The value of x is 28.