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?