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. If the given equation system is impossible to solve, return (None, None).
  def solve_linear_equation_system(a, b, c):
   if a == 0 and b == 0:
   return (None, None)
   x = (c - b) / a if a != 0 else None
   y = (c - a*x) / b if b != 0 else None
   return (x, y)
  assert solve_linear_equation_system(2, 1, 4)==(2.0, 2.0)
  assert solve_linear_equation_system(0, 1, 4)==(None, 4.0)
  assert solve_linear_equation_system(2, 0, 4)==(2.0, None)
  assert solve_linear_equation_system(0, 0, 4)==(None, None)
output: def solve_linear_equation_system(a, b, c):
      if a == 0 and b == 0:
          return (None, None)
      x = (c - b) / a if a != 0 else None
      y = (c - a*x) / b if b != 0 else None
      return (x, y)