input: from typing import Tuple
  
  def objective_function(coeffs: Tuple[float, float], constants: Tuple[float, float]) -> float:
      """
      Calculate the objective function of a linear equation given by ax + by = c.
      
      >>> objective_function((3, 5), (7, 0))
      7.0
      >>> objective_function((2, -1), (4, -1))
      2.0
      """
      a, b = coeffs
      c, _ = constants
      return a * c
  
  # For example:
  result = objective_function((3, 5), (7, 0))
  print(result)
output:     return abs(a * c + b * _)