input: Write a function to solve a linear equation system of the form ax + by = c. The function should take three parameters: a, b, and c, and return the values of x and y as a tuple.
  
  assert solve_linear_equation_system(2, 1, 4) == (2.0, 0.0)
  assert solve_linear_equation_system(1, 1, 2) == (1.0, 1.0)
  assert solve_linear_equation_system(1, -1, 0) == (0.0, 0.0)
  assert solve_linear_equation_system(3, -5, 1) == (2.0, -1.0)
  assert solve_linear_equation_system(0, 1, 2) == None
output: def solve_linear_equation_system(a, b, c):
      if a == 0 and b == 0:
          return None
      elif a == 0:
          return (0.0, c / b)
      elif b == 0:
          return (c / a, 0.0)
      else:
          return (c / a, 0.0)