input: 
  def linear_eq(a: float, b: float, c: float) -> float:
      """ Calculate the objective function of a linear equation given the coefficients a, b, and c.
      The equation is in the form: ax + by = c.
      Return the value of the objective function.
      
      Example:
      >>> linear_eq(3, 5, 7)
      3*x + 5*y - 7
      """
  
output:     return f"{a}*x + {b}*y - {c}"