for Model (II)). Basically, Johnson and Montgomery [12]’s
arguments about the optimal solution are not complete. Sphicas [13] overcomes the shortcomings of Johnson and
Montgomery [12] to use the algebraic approach to get the full analysis about locating the optimal solution without
derivatives and obtain the explicit identification of the two cases. The results of Sphicas [13] are correct and interesting;
however, Sphicas [13] is rather trick such that the process of derivation to locate the optimal solutions is not easy.
Furthermore, he uses some intuitive arguments.