Use Stepping-Stone method for the following:

Malinaw Company, a manufacturer of TV sets, has three manufacturing plants and three main distributors. The per-unit costs of shipping from plant A to distributor 1, 2, and 3 are Php 50, Php 20, and Php 20, respectively. The corresponding costs of shipping from plant B are Php 40, Php 20, and Php 10. The costs from plant C are Php 10, Php 20, and Php 40. Next month, the company expects to have 120 TV sets available at plant A, 130 sets available at plant B, and 200 sets available at plant C. The monthly requirements of distributors 1, 2, and 3 are 100, 250, and 100 sets respectively. The objective is to find the least-cost way of shipping from the three plants to the three distributors.