In a survey of employees at a fast food​ restaurant, it was determined that 13 cooked​ food, 12 washed​ dishes, 22 operated the cash​ register, 5 cooked food and washed​ dishes, 5 cooked food and operated the cash​ register, 7 washed dishes and operated the cash​ register, 2 did all three​ jobs, and 6 did none of these jobs.

a) How many employees were​ surveyed?