Can someone explain how to do this. you

You can extend the lines to give you that in the first picture. When the lines are extended, you'll notice that some angles correspond to the another. Note 113°. It corresponds to the angle close to b.

You can solve for a now (in picture 2).
b + 113° = 180° ( sum of angle on a straight line)
b = 180° - 113°
b = 67°

Do the same thing for to find a. See picture 3.
In picture 4, a + 36° = 180° ( same reason as the one above)
a = 180° - 36°
a = 144°

Hope I was helpful? ☺️