Answer:
Step-by-step explanation:
m∠ABC + m∠BAC + m∠ACB = 180°
a + 2a + 6a = 180°
9a = 180°
a = 20°
m∠ABC = 20°
m∠BAC = 2 × 20° = 40°
m∠ACB = 6 × 20° = 120°
