input: Write a python function to calculate the final grade of a student given their assignment, test, and project scores.
  assert Student(90, 80, 70).calculate_grade() == 80.0
  assert Student(100, 90, 80).calculate_grade() == 90.0
  assert Student(60, 75, 85).calculate_grade() == 75.5
output: class Student:
      def __init__(self, assignment, test, project):
          self.assignment = assignment
          self.test = test
          self.project = project
  
      def calculate_grade(self):
          return (self.assignment * 0.4) + (self.test * 0.4) + (self.project * 0.2)