While reviewing the sample of audit fees, a senior accountant for the firm notes that the fee charged by the firm's accountants depends on the complexity of the return. A comparison of actual charges therefore might not provide the information needed to set next year's fees. To better understand the fee structure, the senior accountant requests a new sample that measures the time the accountants spent on the audit. Last year, the average hours charged per client audit was 3.26 hours. A new sample of 15 audit times shows the following times in hours. Complete parts a and b below. 3.8 2.5 3.1 3.3 4.3 3.8 4.6 4.6 3.3 3.4 4.1 4.4 4.5 4.8 4.7 a) Assume the conditions necessary for inference are met. Find a 90% confidence interval for the mean audit time. The 90% confidence interval to estimate the mean audit time is from 2.64 to 5.28 (Round to two decimal places as needed.)