input: Write a function to solve a linear equation system of the form: ax + by = c. The function should return the values of x and y. If the given coefficients make the equation unsolvable, return None.
  def solve_linear_equation_system(a, b, c):
   if a == 0 and b == 0:
   return 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) is None
  assert solve_linear_equation_system(1, 0, 4) is None
  assert solve_linear_equation_system(0, 0, 4) is None
output: def solve_linear_equation_system(a, b, c):
      if a == 0 and b == 0:
          return None
      x = (c - b) / a if a != 0 else None
      y = (c - a*x) / b if b != 0 else None
      return x, y