In the right panel of Figure 12-2, the dashed a+s curve is obtained when the government gives individual A a subsidy of s=$3 per hour for tending his or his or her yard. Since the MPBa+s curve intersects the MPCa curve at point Es, individual A will be induced to work the socially optimal number of hours (that is, 10 hours) per week in his or her yard, so that the marginal social benefit (MSB=MPBa+MPBb) equals the marginal social cost (MSC=MPCa). Other taxes used to overcome negative externalities or external diseconomies. (and raise revenues to provide government services) are liquor, gasoline taxes. Other subsidies used to correct for positive externalities or external economies are investment tax credit to promote investments, depletion allowances to promote natural resource development, and aid to education.