Construction cost of a wastewater treatment plant is:C=1,300,000*Q^0.65, where Q is the capacity of the plant in million gallons per day, MGD, and C is in dollars.

Demand for plant capacity increases linearly from zero today at 1 MGD per year.

Under the assumption of either 1 or 4 plant expansions (120 MGD or 45 MGD) will occur for the next 20 years, determine the break-even interest rate at which the cost of one expansion exactly equals that of four expansions.

Plot the break-even chart.

Which plant should the city choose should the interest rate be 6%?