Please show the mathematical Formulation (decision variable, objective function, constraints) for this Transshipment Problem and solve using Excel solver.

Consider a company which has seven stores. The company is going to conduct a sales campaign for one of its products. Before the campaign begins, the company must redistribute its inventory of this product. Stores 1 and 4 have an excess stock of 20 and 10 units, respectively, while stores 2,3 , and 7 require 15,8 , and 7 more units, respectively. The inventory at stores 5 and 6 is to remain unchanged. A diagram of the situation with unit shipping cost (cij) associated with each arc is shown in the figure below. Formulate this problem as a linear programming model, and solve it