input: 
  from typing import Tuple
  
  def objective_function(a: float, b: float, c: float, x: float, y: float) -> float:
      """ Calculate the objective function of a linear equation ax + by - c.
      >>> objective_function(3.0, 5.0, 7.0, 2.0, 1.0)
      4.0
      >>> objective_function(1.0, 1.0, 0.0, 0.0, 0.0)
      0.0
      """
      return a * x + b * y - c
  
output:     return a * x + b * y - c