The five nodes in the following network represent points one year apart over a four-year period. Each node indicates a time when a decision is made to keep or replace a firm's computer equipment. If a decision is made to replace the equipment, a decision must also be made as to how long the new equipment will be used. The arc from node O to node 1 represents the decision to keep the current equipment one year and replace it at the end of the year. The arc from node O to node 2 represents the decision to keep the current equipment two years and replace it at the end of year 2 . The numbers above the arcs indicate the total cost associated with the equipment replacement decisions. These costs include discounted purchase price, trade-in value, operating costs, and maintenance costs. Use linear programming to determine the minimum cost equipment replacement policy for the four-year period