Не могу решить задачу?
Ну так всё правильно. Количество дней же ты НЕ СЧИТАЕШЬ.
Ты, похоже, вообще не понимаешь что этот код делает.may_2017 = [24, 26, 15, 10, 15, 19, 10, 1, 4, 7, 7, 7, 12, 14, 17, 8, 9, 19, 21, 22, 11, 15, 19, 23, 15, 21, 16, 13, 25, 17, 19]
may_2018 = [20, 27, 23, 18, 24, 16, 20, 24, 18, 15, 19, 25, 24, 26, 19, 24, 25, 21, 17, 11, 20, 21, 22, 23, 18, 20, 23, 18, 22, 23, 11]

def comfort_count(temperatures):
    k = 0
    for temp in temperatures:
        if temp >= 22 and temp <= 26:
              k = k + 1
    print(k)

comfort_count(may_2017)  
comfort_count(may_2018)
may_2017 = [24, 26, 15, 10, 15, 19, 10, 1, 4, 7, 7, 7, 12, 14, 17, 8, 9, 19, 21, 22, 11, 15, 19, 23, 15, 21, 16, 13, 25, 17, 19]
may_2018 = [20, 27, 23, 18, 24, 16, 20, 24, 18, 15, 19, 25, 24, 26, 19, 24, 25, 21, 17, 11, 20, 21, 22, 23, 18, 20, 23, 18, 22, 23, 11]

# допишите код ниже
def comfort_count(temperatures):
    count = 0
    for temp in temperatures:
        if 21 < temp <27:
            count += 1
    print('Количество комфортных дней в этом месяце:', count)
# дальше код не меняйте
comfort_count(may_2017)  # узнаем, что было в мае 2017 г.
comfort_count(may_2018)  # узнаем, что было в мае 2018 г