Question 320112
If 31 people owned a truck and 22 owned both a truck and car, then 31-22 = 9 people owned just a truck. Likewise, 62-22=40 people owned just a car. So the total number of people interviewed was:

(people who own just trucks) + (people who own just cars) + (people who own both) + (people who own neither) = 
9 + 40 + 22 + 9 = 80 people