input: def linear_eq(a: float, b: float, c: float, x: float, y: float) -> float:
      """ Calculate the value of the objective function of a linear equation given the coefficients
      a, b, c and the variables x and y.
      >>> linear_eq(3, 5, 7, 1, 1)
      1
      >>> linear_eq(3, 5, 7, 2, 2)
      7
      """
output:     return a * x + b * y + c