A coal-fired power plant produces power with costs . Each unit of power earns the plant . Burning coal releases particulate matter (PM2.5), a pollutant that is known to cause heart disease, lung disease, and birth defects. The coal plant borders a wildlife sanctuary which sells tourism visits for a price $30. However, the sanctuary's animals are getting sick due to the negative externality of PM2.5, such that the costs to the sanctuary are . The local government decides to tax the coal plant to internalize its negative externality. What tax will restore the social optimum?