What is –9 – (–13) and how do i solve

What could explain what happened when the time was equal to 120 minutes

The administrator of a large assisted living facility wanted to know the average age of the residents living at the facility. he randomly selected 12 residents and determined their age, listed here: 80, 65, 75, 83, 68, 73, 88, 79, 94, 72, 79, 68 what's the average age of the sample of residents? a. 79 years old b. 68 years old c. 75 years old d. 77 years old

Can someone check if i did this right since i really want to make sure it’s correct. if you do you so much