Help pls. I don't understand where i wrong...

lloyd = {

"name": "Lloyd",

"homework": [90.0, 97.0, 75.0, 92.0],

"quizzes": [88.0, 40.0, 94.0],

"tests": [75.0, 90.0]

}

alice = {

"name": "Alice",

"homework": [100.0, 92.0, 98.0, 100.0],

"quizzes": [82.0, 83.0, 91.0],

"tests": [89.0, 97.0]

}

tyler = {

"name": "Tyler",

"homework": [0.0, 87.0, 75.0, 22.0],

"quizzes": [0.0, 75.0, 78.0],

"tests": [100.0, 100.0]

}

# Add your function below!

def average(numbers):

sum(numbers)

total = float(sum(numbers))

a = total / len(numbers)

return a

def get_average(student):

homework = average(student["homework"])

quizzes = average(student["quizzes"])

tests = average(student["tests"])

return 0.1*homework+\

0.3*quizzes+\

0.6* tests

def get_letter_grade(score):

if score>=90:

return "A"

elif score>=80:

return "B"

elif score>=70:

return "C"

elif score>=60:

return "D"

else:

return "F"

print get_letter_grade(get_average(lloyd))

def get_class_average(students):

results = []

results.append(get_average(students))

return average(results)

Oops, try again.

get_class_average([alice]) resulted in an error: list indices must be integers, not str