I keep getting an error which says:"Oops, try again. One of the following is missing or broken when we tried to use it: alice, lloyd, tyler, students, get_class_average, get_letter_grade"

Can someone please help me?

```
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):
total=sum(numbers)
total=float(total)
return total/len(numbers)
def get_average(student):
homework=0.1*average(student["homework"])
quizzes=0.3*average(student["quizzes"])
tests=0.6*average(student["tests"])
return homework+quizzes+tests
def get_letter_grade(score):
return "A" if score>=90 else "B" if score>=80 else "C" if score>=70 else "D" if score>=60 else "F"
def get_class_average(students):
results = []
for student in students:
results.append(get_average(student))
return average(results)
print get_class_average([lloyd, alice, tyler])
print get_letter_grade(get_class_average([lloyd, alice, tyler]))
```