question: Last Friday, 13 of the 82 teachers at Rydell Elementary School were sick. There were 9 substitute teachers called in to help. How many teachers were at school that day?
answer: There were 82 – 13 = <<82-13=69>>69 regular teachers at school.
  If we add the substitute teachers, we find there were 69 + 9 = <<69+9=78>>78 teachers at school that day.
  #### 78