Answer:
∠B = 132°
Step-by-step explanation:
Quadrilateral ABCD is inscribed in the given circle.
And if a quadrilateral is inscribed inside a circle then the quadrilateral is called cyclic quadrilateral.
And the sum of opposite angles of a cyclic quadrilateral is supplementary that is 180
⇒ Sum of opposite angles of the quadrilateral ABCD is 180
⇒ ∠A + ∠C = 180° and ∠B + ∠D = 180°
Now, ∠B + ∠D = 180°
⇒ 3x - 12 + x = 180
⇒ 4x - 12 = 180
⇒ 4x = 180 + 12
⇒ 4x = 192
⇒ x = 48
So, ∠B = 3x - 12
⇒ ∠B = 3 × 48 - 12
⇒ ∠B = 144 - 12
⇒ ∠B = 132°
