You are given a transportation problem. Specifically, S1 and S2 are the two sources to supply goods to D1 and D2, which are the destinations, through two intermediate stops, I1 and I2, i.e. S1, S2, D1, D2, I1 and I2 are cities.
The maximum supplies (A1 and A2), the minimum demands (B1 and B2), and the maximum storage capacities (M1 and M2) are constants. (I don't give you the actual numbers, and I use symbols to represent them.) All the six numbers are non-negative integers. The costs of each route (i.e., aij and bij) are specified on each link in the diagram. Again, these costs are constants. I do not give you the actual numbers. I use symbols to represent them. They are non-negative numbers.
You are asked to develop a linear programming model that calculates the numbers of items to be transported through each route to minimize the transportation costs. To answer this question, you write down an objective function, and a set of constraints, to formulate this problem. You are not expected to calculate the optimal solution