$$

Each hour, an average of $900$ cars enter the network in Figure $46$ at node $1$ and seek to travel to node $6.$ The time it takes a car to traverse each arc is shown in Table $31.$ In Figure $46,$ the number above each arc is the maximum number of cars that can pass by any point on the arc during a one$-$hour period. Formulate an MCNFP that minimizes the total time required for all cars to travel from node $1$ to node $6.$