How many adults must be randomly selected to estimate the mean FICO (credit rating) score of working adults in the United States. We want 90% confidence that the sample mean is within 6 points of the...

How many adults must be randomly selected to estimate the mean FICO (credit rating) score of working adults in the United States. We want 90% confidence that the sample mean is within 6 points of the population mean. Assume that the population standard deviation is 78.