Much of the nation's coal is extracted by strip mining. this process leaves a huge barren hole in the ground when complete, and the cost of replanting the trees is approximately $10 per ton of coal. burning the coal for electricity causes air pollution. no one knows how much damage the air pollution causes, but we know that for another $10 per ton the power plant can be outfitted with a pollution control device. what is one measure of the true social cost of coal fired electricity, in dollars per ton?