In figure $ a=40°$. The value of $ b$ is
20°
24°
36°
120°
Explanation for the correct option:
Given, a=40°
Then,2a=2×40=80°
We know that, the angles formed on the starlight line are equal to 180°
Then,5b+2a=180°
⇒5b+80=180
⇒ 5b=180-80
⇒ 5b=100
⇒ b=1005
⇒ b=20°
Hence the correct option is option(A)