Explanation:
A circle is 360 degrees
209 is part of the circle so find the difference between 360 and 209
360 - 209 = 151
If the two angles are equivalent to 151, then we find the difference between 151 and 96 to get the measurement for angle b
151 - 96 = 55
I read now that it says use the rules above, but I'm not seeing any rules in the picture so hopefully my steps are the rules you're referring to