Dry bleach. The net weight (in ounces) of boxes of dry bleach are monitored by taking samples of 4 boxes from each hour's production. The process mean should be µ = 16 oz. Past experience indicates that the net weight when the process in properly adjusted varies with σ = 0.4 oz. The mean weight for each hour's sample is plotted on an x control chart. Calculate the center line and control limits for this chart.