Consider the transportation problem having the following parameter table:

After several iterations of the transportation simplex method, a BF solution is obtained that has the following basic variables: x13 20, x21 25, x24 5, x32 25, x34 5, x42 0, x43 0, x45 20. Continue the transportation simplex method for two more iterations by hand. After two iterations, state whether the solution is optimal and, if so, why.