Answer:
So the mean means the average of all the numbers, right? So that means all you have to do is add up all the numbers together, and divide by the amount of numbers there are.
so for this question...
17 + 24 + 26 + 13 = 80.
since it equals 80, and there are four numbers, (17, 24, 26, 13) divide 80/4.
80/4 = 20
your answer is 20!
I hope this helps!