Let L Represent the Number of Workers Hired by a Firm

Let L represent the number of workers hired by a firm, and let Q represent that firm's quantity of output. Assume two points on the firm's production function are (L = 12, Q = 122) and (L = 13, Q = 130) . Then the marginal product of the 13th worker is

A) 8 units of output.
B) 10 units of output.
C) 122 units of output.
D) 132 units of output.