input: Below is an instruction that describes a task. Write a response that appropriately completes the request.
  
  ### Instruction:
  Using Python, create a function that calculates the objective function of a linear equation.
  
  ### Input:
  ax + by = c
  
  a = 3, b = 5, c = 7
  
  ### Output:
  def linear_eq(a: int, b: int, c: int, x: int, y: int) -> int:
      """Calculate the objective function of a linear equation ax + by = c.
      >>> linear_eq(3, 5, 7, 2, 1)
      6
      >>> linear_eq(3, 5, 7, 4, 1)
      10
      """
      return a*x + b*y - c
output:     return a*x + b*y - c