Find the rate per hour for each of the four asked by diving the total by the number of hours:
Mark: 100 /10 = $10 per hour
Rick: 80 / 9 = $8.89 per hour
Steve: 75 / 8 = $9.38 per hour
Andy: 60 / 5 = $$12 per hour
Now add the four hourly rates and divde by 4:
10 + 8.89 + 9.38 + 12 = 40.27 / 4 = 10.07
Rounded to the nearest whole dollar would be $10 per hour.
The answer is A.