Step-by-step explanation:
[tex] \frac{360 - 2(99)}{2} = \\ = \frac{360 - 198}{2} = \\ = \frac{162}{2} = \\ = 81[/tex]
Answer: 81°
Angles on a straight line always add up to 180°.
So as a and 99° are on the same straight line you would have to do 180-99=81°
Hope this helps :)
