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 = 
<gadget id="calculator">82-13</gadget>
<output>69</output>
69 regular teachers at school.
If we add the substitute teachers, we find there were 69 + 9 = 
<gadget id="calculator">69+9</gadget>
<output>78</output>
78 teachers at school that day.

<result>78</result>