Can you give me some step-by-step instructions for this math problem: 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?
There were 82 – 13 = 69 regular teachers at school.
If we add the substitute teachers, we find there were 69 + 9 = 78 teachers at school that day.