In a production process for canvas, a sample consisting of 25 square feet contains 4 discolored spots that must be touched up before shipping. Data for this and subsequent samples, each consisting of 25 square feet of canvas, are shown here. Use an appropriate 3-sigma control chart in determining whether the process is in control.

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Sample Number of Spots Number of Spots Number Sample Number 16 13 18 19 20 21 12 10 12 23 24 25 26 27 12 15 12 13 14 15 12 30 16