Answer:
Use the "find vertically opposite angle" method.
a = 80°
To find the other angles:
Since the angles equal up to 360 which makes a full circle shape...
360 - 80 - 80 = 200 (B and C)
200 ÷ 2 = 100 (Angle for B and C since they are vertically opposite, hence having the same angle)
b = 100°
c = 100°