Assume that the current global demand for fossil fuel (in billions of barrels per year) is given by the equation:

Q = 400 - P

and the current world supply of oil is given as

Q = -100 + 4P

If the dollar value of the marginal environmental damage associated with burning fossil fuels is given as

MD = 1.25Q

what quantity characterizes the efficient market outcome for fossil fuels? That is, what would be the quantity of fossil fuels will be sold if the market reflected both the private and external costs of fossil fuel use?