If m∠abc = 70°, what is m∠abd? justify your reasoning.
  using the addition property of equality, 40 + 70 = 110, so m∠abd = 110°. 
using the subtraction property of equality, 70 − 30 = 40, so m∠abd = 30°. 
using the angle addition postulate, 40 + m∠abd = 70. so, m∠abd = 30° using the subtraction property of equality.
  using the angle addition postulate, 40 + 70 = m∠abd. so, m∠abd = 110° using the addition property of equality.