Concept:Marginal cost is the additional cost of producing one more unit of output.Explanation:At output level 3, total cost is P=$750+$900=$1650.At output level 2, the total cost is given as $1310.The unknown Q is the marginal cost of increasing output from 2 units to 3 units.Therefore, Q=$1650−$1310=$340.Answer:Q=$340, so the correct option is B.