A company is concerned about the diameter of one of its steel pipes. They took 10 daily samples with 10 observations each and obtained the following sample means: 15.0, 16.4, 13.8, 14.6, 17.2, 15.2, 15.0, 16.9, 17.9, and 16.5. If the average range for the samples was 2 inches, what are the upper and lower control limits for the X-bar chart?