input: Write a function to solve a linear equation system of the form: ax + by = c, where the function takes in three parameters a, b, and c. It should return the values of x and y as a tuple.
  
  def solve_linear_equation_system(a, b, c):
      x = (c - b) / a
      y = (c - a*x) / b
      return x, y
  
  assert solve_linear_equation_system(2, 1, 4) == (2.0, 2.0)
  assert solve_linear_equation_system(3, 2, 7) == (1.0, 2.0)
  assert solve_linear_equation_system(1, 1, 5) == (5.0, 0.0)
  assert solve_linear_equation_system(1, -1, -1) == (None, None)
  assert solve_linear_equation_system(0, 0, 0) == (None, None)
output: def solve_linear_equation_system(a, b, c):
      if a == 0 and b == 0:
          return None, None
      if a == 0:
          y = c / b
          return None, y
      if b == 0:
          x = c / a
          return x, None
      x = (c - b) / a
      y = (c - a*x) / b
      return x, y