9) b and 50 are supplementary angles so the sum is equal to 180°. So:
[tex]\begin{gathered} b+50=180 \\ solve\text{ for b} \\ b+50-50=180-50 \\ b=130 \end{gathered}[/tex]
Answer 9: b = 130°
10) They are opposite angles at the vertex, which means that they have equal measure. Then:
[tex]b=43[/tex]
Answer 10: b = 43°
11) We know that a complete angle measures 360° therefore:
[tex]\begin{gathered} b+96+209=360 \\ simplify \\ b+305=360 \\ solve\text{ for b} \\ b+305-305=360-305 \\ b=55 \end{gathered}[/tex]
Answer 11: b = 55°
12) These are complementary angles so the sum is equal to 90°. Therefore:
[tex]\begin{gathered} b+63=90 \\ solve\text{ for b} \\ b+63-63=90-63 \\ b=27 \end{gathered}[/tex]
Answer 12: b = 27°
