29. One difficulty with solving the general minimum-cost ow problem with upper and lower bounds on the variables lies in determining an initial basic feasible solution. Show that an initial basic feasible solution to this problem can be determined by solving an appropriate maximum-ow problem. ( Hints. (1) Make a variable substitution to eliminate the nonzero lower bounds on the variables. (2) Form a \"super source,\" connected to all the source nodes, and a \"super sink,\" connected to all the sink nodes, and maximize the ow from super sink to super source.)