Please help me do excel calculations and graphs, show the formulas

Suppose a process has been monitored daily for the last ten days and the number of machine failures each day was noted. The results follow:

Day Number: 1 2 3 4 5 6 7 8 9 10

Number of Failures: 8 9 6 10 12 4 9 11 9 12

Compute control limits for a c-chart at 3 sigma level that monitors the average number of machine failures per day. Draw the chart and plot the data. Is the process under control?