A food processing plant packages butter in blocks that are supposed to contain 454 grams (one pound). The quality control department regularly takes samples of 40 blocks and finds the mean weight to see if it is 454 grams or above. If the standard deviation of the packaging machine is calibrated to be 3.1 grams, find the mean weight of butter the machine should package so that the probability that quality control finds the sample mean weight is less than 454 grams is less than 2%?