4.18 The following table provides estimates for the recent values of the costs of additional wastewater treatment plant capacity nee- ded at the end of each 5-year period for the next 20 years. Find the capacity expansion schedule that minimizes the present values of the total future costs. If there is more than one least-cost solution, indicate which one you think is better, and why? Discounted cost of additional capacity Units of additional capacity 2 4 6 8 Total required capacity at end of period 10 Period years 1 1-5 12 15 18 23 26 2 2 8 11 13 15 6 6- 10 3 11- 6 8 8 15 4 10 16- 4 20 4.18 The following table provides estimates for the recent values of the costs of additional wastewater treatment plant capacity nee- ded at the end of each 5-year period for the next 20 years. Find the capacity expansion schedule that minimizes the present values of the total future costs. If there is more than one least-cost solution, indicate which one you think is better, and why? Discounted cost of additional capacity Units of additional capacity 2 4 6 8 Total required capacity at end of period 10 Period years 1 1-5 12 15 18 23 26 2 2 8 11 13 15 6 6- 10 3 11- 6 8 8 15 4 10 16- 4 20