input: Write a python function to calculate the average grade of a student using the provided Student class.
  assert Student("John", [80, 90, 85, 95]).calculate_grade() == 88.75
  assert Student("Alice", [70, 75, 80, 85]).calculate_grade() == 77.5
  assert Student("Bob", [60, 65, 70, 75]).calculate_grade() == 67.5
output: class Student:
      def __init__(self, name, grades):
          self.name = name
          self.grades = grades
  
      def calculate_grade(self):
          return sum(self.grades) / len(self.grades)