John is the only manufacturer of a product that increases the efficiency of refrigerators. He is the only company that makes and supplies this good and his goal is to maximize profits. According to economic theory, how would John determine the price of his device? Please explain why

He would set price where the supply curve intersects with the demand curve.

He would set price where demand is unit elastic.

He would set price where marginal revenue = marginal cost.

He would set price above marginal cost, anywhere on the demand curve.