In a study relating the amounts of time required for room service delivery at a newly opened

Question:

In a study relating the amounts of time required for room service delivery at a newly opened Radisson Hotel, 20 deliveries had a mean time of 24.2 min and a standard deviation of 8.7 min. The sample data appears to have a bell-shaped distribution. Find the 90% confidence interval for the mean time of all deliveries.