input: Write a python function to create a MathOperations class that can add and subtract two numbers.
  assert MathOperations(5, 3).add() == 8
  assert MathOperations(5, 3).subtract() == 2
  assert MathOperations(10, 0).add() == 10
  assert MathOperations(10, 0).subtract() == 10
output: class MathOperations:
      def __init__(self, a, b):
          self.a = a
          self.b = b
      
      def add(self):
          return self.a + self.b
  
      def subtract(self):
          return self.a - self.b