Answer:
131°
Step-by-step explanation:
Sum of all angles of a quadrilateral = 360°
We can find the unknown angle ∠B, by subtracting the sum of the angles ∠A, ∠C, ∠D from 360°.
∠A + ∠B + ∠C + ∠D = 360
105 + ∠B + 34 + 90 = 360
∠B + 229 = 360
∠B = 360 - 229
∠B = 131°