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? ☺️