A company manufactures a product at its plants in A, B, C, and D, then ships the product to four customers in P, Q, R, and S, The monthly capacity of plants A, B, C, and D are 4500, 7800, 10400, and 4800 units, respectively. The monthly demand from customers P, Q, R, and S are 3700, 10100, 4600, and 7900 units, respectively. Use Excel Solver to find the optimal distribution plant that will give the lowest total monthly shipping cost if the shipping cost per unit (in dollars per unit) are as follows: - - from A to P, Q, R, and from B to P, Q, R, and from C to P, Q, R, and from D to P, Q, R, and S are 12, 9, 6, and 7 dollars per unit, respectively; S are 20, 13, 9, and 4 dollars per unit, respectively; S are 3, 6, 7, and 12 dollars per unit, respectively; S are 15, 11, 4, and 9 dollars per unit, respectively. The optimal total shipping costs is dollars per month.