Modify Prob. 6.76 into an economic analysis, as follows. Let the 40 m of wrought iron pipe have a uniform diameter d. Let the steady water flow available be Q = 30 m3/h. The cost of the turbine is $4 per watt developed, and the cost of the piping is $75 per centimeter of diameter. The power generated may be sold for $0.08 per kilowatt hour Find the proper pipe diameter for minimum payback time, i.e., minimum time for which the power sales will equal the initial cost of the system.