a popular author brings 8428 copies of her new book on her book tour. She sells 85 books at each book signing. She makes two estimates to determine how many books signing. She makes two estimates to determine how many book signings it will take to sell all of her books: 8400/70=120 and 8100/90=90.

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.