9. Arrow Airlines has attempted to streamline the process of booking flight reservations in order to service the maximum number of on-site customers. The manager has timed 40 transactions from the time the agent begins talking with the customer until tickets are prepared and paid for and luggage is checked in. The mean time is 4.7 minutes, and the estimated standard deviation is 1.8 minutes. How many observations are required to estimate the mean time with 95 percent confidence within an accuracy of 0.50 minute?