The daily revenues of a cafe near the university are approximately normally distributed. The owner recently collected a random sample of 40 daily revenues and found a 90% confidence interval for the average daily revenues in his shop is (973.993, 1026.007). He is unsatisfied by the precision of this confidence interval, however, and wishes to reduce the margin of error by a factor of 2, while retaining the same level of confidence. What sample size do you suggest he use to obtain the desired margin of error