Answer: 82.4167 (approximate)
Explanation
Given data set = {71,73,77,82,88,91,92,92,89,84,78,72}
Add up the values:
71+73+77+82+88+91+92+92+89+84+78+72 = 989
Divide that sum by the sample size 12 to get the sample mean.
989/12 = 82.416666.... where the 6's go on forever.
If we round to say 4 decimal places, then we get 82.4167. Round this however your teacher instructs.