21. A discount car rental agency purchases new cars of a certain model type and keeps them a maximum of four years before replacement. Suppose a new car costs Php 80,000 and that the annual maintenance cost and salvage value figures are as shown below. The final maintenance cost figure reflects the much higher maintenance expense for these relatively high-mileage cars in their fourth year of operation. Year of Operation 2 1 3 4 2.000 3.000 5,000 10,000 Annual Maintenance Cost Php Salvage Value Php 60,000 45,000 35,000 25,000 Determine the optimal replacement schedule, over a four-year period, for a new car purchased now. Assume that the given cost figures do not change during the period of interest. Use the appropriate NETWORK ALGORITHM to solve this problem. 21. A discount car rental agency purchases new cars of a certain model type and keeps them a maximum of four years before replacement. Suppose a new car costs Php 80,000 and that the annual maintenance cost and salvage value figures are as shown below. The final maintenance cost figure reflects the much higher maintenance expense for these relatively high-mileage cars in their fourth year of operation. Year of Operation 2 1 3 4 2.000 3.000 5,000 10,000 Annual Maintenance Cost Php Salvage Value Php 60,000 45,000 35,000 25,000 Determine the optimal replacement schedule, over a four-year period, for a new car purchased now. Assume that the given cost figures do not change during the period of interest. Use the appropriate NETWORK ALGORITHM to solve this