US drivers consume billions of gallons of gas every week, and with every gallon consumed harmful emissions are released into the atmosphere. The aggregate demand function for gasoline is given by P = 12 2QD, where Q is the quantity of gallons of gas per week in billions and P reflects the price per gallon in dollars. The aggregate supply function is given by P = 1 + QS . IMF economists have estimated a substantial external marginal damage of gas consumption, which we'll round to $1 per gallon