Anderson Windows produces vinyl-coated aluminum windows. A thickness of 15 mm for the vinyl coating is required in order for the windows to seal properly and not jam. The standard deviation of their process for coating the windows is 1.2 mm. Their quality control procedure is to take a sample of 4 windows every 24 hours, measure the vinyl thickness of each, and compute the sample mean. Assume that the distribution of vinyl thickness is normally distributed. The process would be considered to be out of control if the sample mean was greater than ________.