A coffee shop owner wants to know how long customers spend in the shop during their visits. She records the following times (in minutes) for a sample of 20 customers: 23, 42, 15, 28, 19, 34, 37, 40, 28, 16, 21, 38, 31, 27, 19, 23, 32, 25, 33, 35. Construct a stem and leaf plot for the data, and describe the results.