9) b and 50 are supplementary angles so the sum is equal to 180°. So:
Answer 9: b = 130°
10) They are opposite angles at the vertex, which means that they have equal measure. Then:
Answer 10: b = 43°
11) We know that a complete angle measures 360° therefore:
Answer 11: b = 55°
12) These are complementary angles so the sum is equal to 90°. Therefore:
Answer 12: b = 27°