input: def solve_linear_equation_system(a: float, b: float, c: float) -> tuple:
      """ Solve a linear equation system of the form ax + by = c.
      >>> solve_linear_equation_system(2, 1, 4)
      (2.0, 2.0)
      >>> solve_linear_equation_system(1, 3, 9)
      (9.0, 0.0)
      >>> solve_linear_equation_system(3, -1, 5)
      (2.0, -1.0)
      """
      x = (c - b) / a
      y = (c - a*x) / b
      return x, y
output:     x = c / a
      y = 0
      return x, y