input: Write a python function to calculate the tax for a user based on their salary using the given User class.
  assert User("Alice", 10000).get_tax() == 0
  assert User("Bob", 20000).get_tax() == 1500
  assert User("Charlie", 60000).get_tax() == 12000
  assert User("David", 50000).get_tax() == 7500
output: class User:
      def __init__(self, name, salary):
          self.name = name
          self.salary = salary
  
      def get_tax(self):
          if self.salary <= 10000:
              return 0
          elif self.salary <= 30000:
              return (self.salary - 10000) * 0.075
          elif self.salary <= 60000:
              return 1500 + (self.salary - 30000) * 0.15
          else:
              return 6000 + (self.salary - 60000) * 0.25