Final answer:
The socially efficient amount of steel to produce is 46 million tons, and the socially efficient price is $254 per ton.
Step-by-step explanation:
The socially efficient amount of steel to produce can be determined by finding the intersection of the marginal cost and marginal external cost curves. The industry supply curve represents the marginal cost of producing steel, which is given by MC = 20 + 2Q. The marginal external cost of pollution emitted during production is represented by MEC = 66 + Q.
To find the socially efficient quantity, we need to equate MC and MEC:
20 + 2Q = 66 + Q
Solving this equation, we find Q = 46 million tons.
The socially efficient price can be found by substituting the socially efficient quantity into the inverse demand curve:
P = 300 - Q = 300 - 46 = $254 per ton.