Answer:
∠B = 82°
Step-by-step explanation:
(see attached for reference)
recall the property that an exterior angle of a triangle is equal to the sum of its two remote interior angles.
in our case, the exterior angle is obtuse ∠A = 143°
the two remote interior angles are ∠C and ∠B
hence according to our definition above:
143° = ∠C + ∠B (we are given that ∠C =61°)
hence
143° = 61° + ∠B
143° - 61° = ∠B
∠B = 82°
