7.19. A maintenance group improves the effectiveness of SS its repair work by monitoring the number of main- tenance requests that require a second call to com- plete the repair. Twenty weeks of data are shown in Table 7E. 7. Table 7E.7 Data for Exercise 7.19 Second Second Total Visit Total Visit Weak Requests Required Wook Requests Required 1 200 6 11 100 2 250 8 12 100 3 250 13 100 4 250 7 14 200 5 200 3 15 200 5 6 200 16 200 3 150 17 200 10 - N 8 150 18 200 4 9 150 19 250 10 150 N 20 250 a. Find trial control limits for this process. b. Design a control chart for controlling future pro- duction