Inter-State Moving and Storage Company wishes to establish a control chart to monitor the proportion of residential moves that result in written complaints due to late delivery, lost items, or damaged items. A sample of 55 moves is selected for each of the last 12 months. The number of written complaints in each sample is 7, 6, 6, 7, 4, 7, 10, 5, 6, 4, 8, and 15.