Good afternoon, could someone explain how to do this problem by the Binomial Theorem method

1.The following data represent the time, in minutes, that a patient has to wait for 12 visits to a doctor's office before being seen by her: 17, 15, 20, 20, 32, 28, 12, 26, 25 , 25, 35, 24. Use the sign test at the .05 level of significance to test the doctor's claim that the mean wait time for her patients is no more than 20 min before entering the office.