input: def linear_eq(a: float, b: float, c: float, x: float, y: float) -> float:
      """ Calculate the objective function of a linear equation of the form ax + by = c.
      The function takes in the coefficients a, b, and c, and the variables x and y.
      It returns the value of the objective function a*x + b*y - c.
      >>> result = linear_eq(3, 5, 7, 1, 1)
      -1
      >>> result = linear_eq(3, 5, 7, 0, 0)
      -7
      """
output:     return a * x + b * y - c