input: def linear_eq(a: float, b: float, c: float) -> float:
      """Calculate the objective function of a linear equation.
      The equation is: ax + by = c
      >>> linear_eq(3.0, 5.0, 7.0)
      1.0
      >>> linear_eq(2.0, 4.0, 10.0)
      -2.0
      """
output:     return (c - b) / a if a != 0 else float('inf')