Not sure about this one.

The following data are for a series of increasingly extensive flood-control projects. Total Benefit Per Total Cost Per Year Year Plan A = Levees $ 10,090 $ 16,600 Plan B = Small Reservoir 24,060 36,600 Plan C = Medium Reservoir 44 ,090 52,000 Plan D = Large Reservoir 72,060 64,900 For Plan C marginal costs and marginal benefits are$20,000 and $16,000, respectively. $10,000 and $16,000, respectively. $44,000 and $52,000, respectively. $8,000 and $4,000, respectively