An oil company wants to create lube oil, gasoline and diesel fuel at two refineries. There are two sources of crude oil. Consider arc $2-4.$ The per unit shipping cost of crude B from source $2($node $2)$ to refinery $2($node $4)$ is $$11$ and the yield is $85$ percent. The following flowchart depicts this problem. What is the balance of flow constraint for node $7($Diesel$)?$