• I don't understand what is wrong here =(

Question related to mission The Ship Teams

 
def two_teams(sailors):

a = [] #firstship

b = [] #secondship

for i in range(101):

 if sailors[i] > 40 and sailors[i] < 20:
    a.append[i]

    a.sort

 else: 

    b.append[i]

    b.sort

return a , b