AutoTrader.com would like to test if a difference exists in the age of three different types of vehicles currently on the road: trucks, cars, and vans. The following data represent the age of a random sample of trucks, cars, and vans.

Trucks Cars Vans

12 8 3

8 13 7

9 10 6

11 7 8

The grand mean for these observations is ________.

Group of answer choices

9.3

7.2

8.0

8.5