4. (10 points) The figure below shows the marginal pollution control costs per ton for a single firm. Suppose a tax of Ti per ton is implemented. What would be the net gain to society of the pollution tax versus a command-and-control policy that forced the firm to reduce pollution all the way up to 100 tons? (You can answer this in words and using the areas of the figure.) D 1 1 A B C 30 100