Using it's formula, it is found that the mean of the data set is of 4.1 shirts.
In this problem, the 12 observations are: 3, 4, 8, 5, 2, 5, 0, 5, 3, 4, 3, 7
Hence:
[tex]M = \frac{3 + 4 + 8 + 5 + 2 + 5 + 0 + 5 + 3 + 4 + 3 + 7}{12} = 4.1[/tex]
The mean of the data set is of 4.1 shirts.
For more on the mean of a data-set, you can check https://brainly.com/question/24628525