<h3>Answer: 78.6</h3>
Work Shown:
Multiply across the rows to form a third column. Example: 9*90 = 810 in the first row.
The values in the third column add to 810+1440+1050 = 3300
Divide this over the total number of people which is 9+18+15 = 42
The mean is 3300/42 =78.571 approximately which rounds to 78.6