Question 9 What is the net social benefit of cleaning up the lake at the socially efficient level? Explain how you reached your answer. (Hint: you can use both A and B to calculate) The demand curve (marginal benefit of clean up) shown for questions 6 through 8 (above) is constructed from each household's willingness to pay for water quality. Use this table and the graph above to answer questions 9 and 10. Willingness-to-pay for improved water quality ($) DO Increase (ppm) C D $7 $6 $3 $2 3 3 1. B. in 2. 1. 2. 4. 5.