input: def solve_linear_equation_system(a: float, b: float, c: float):
      """Solves a linear equation system of the form: ax + by = c.
      Returns the values of x and y.
      >>> solve_linear_equation_system(2, 1, 4)
      (2.0, 2.0)
      """
      x = (c - b) / a
      y = (c - a*x) / b
      return x, y
output:     if a == 0 and b == 0:
          raise ValueError("Both coefficients a and b cannot be zero.")
      if a == 0:
          y = c / b
          return None, y
      if b == 0:
          x = c / a
          return x, None