Problem: A river has been used to irrigate farm land. A 3000 megawatt, coal-fired electric generating plant which would require about 40,000 acre-feet of water per year from the river. Operating the generating plant would mean less water for agriculture.
The first part of the question is: which is more efficient use of the water from the river growing food or generating electricity. The part that is giving me trouble is comparing the value of food with the value of electricity.