Tire production

Inspect 15 tires every half an hour for tire production, record the unqualified number of 15 products, test 14 times in total (number of subgroups), and establish a U-chart.

The data are as follows:

15 4

15 5

15 3

15 6

15 2

15 1

15 5

15 6

15 2

15 4

15 7

15 5

15 2

15 3