Maximum flow problem

What is the proper specification of all the variable and parameter

The following table shows that the daily amounts of supply at the FarmA and Farm B and demand of the four retailers A, B, C, D (in thousands of pounds) The cell entries of the table specify the daily capacities of the associated routes. Retailers A B D Farm A Max Supply 50 10 5 0 7 Farm B 4 0 8 30 Max Demand 20 10 10 20 The following table shows that the daily amounts of supply at the FarmA and Farm B and demand of the four retailers A, B, C, D (in thousands of pounds) The cell entries of the table specify the daily capacities of the associated routes. Retailers A B D Farm A Max Supply 50 10 5 0 7 Farm B 4 0 8 30 Max Demand 20 10 10 20