Answer:
see explanation
Explanation:
∠ a and 150° are a linear pair and sum to 180° , then
∠ a + 150° = 180° ( subtract 150° from both sides )
∠ a = 30°
the sum of the 3 angles in a triangle = 180° , then
∠ b + ∠ a + 60° = 180° , that is
∠ b + 30° + 60° = 180°
∠ b + 90° = 180° ( subtract 90° from both sides )
∠ b = 90°