def separate(grades)
that has one parameter - list of grades in the class. The function creates and RETURNS 3 new lists - list of failing grades (grades below 60), list of A grades (90 and above) and the rest of the grades (between 60 and 89).
Write a program that randomly generates the list of grades of size 15, calls function separate, and then prints THREE lists: failing grades, list of A grades, and the rest of the grades.