Annie Quan is a nurse on the evening shift from 10:00 p.m. to 6:00 a.m. at Community Hospital. She is responsible for 15 patients in her area. She averages two calls from each of her patients every evening (Poisson distributed), and she must spend an average of 10 minutes (negative exponential distribution) with each patient who calls. Nurse Quan has indicated to her shift supervisor that although she has not kept records, she believes her patients must wait about 10 minutes on average for her to respond and she has requested that her supervisor assign a second nurse to her area. The supervisor believes 10 minutes is too long to wait, but she does not want her nurses to be idle more than 40% of the time. Determine what the supervisor should do.