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 = 5, Q = 97) and (L = 6, Q = 152). Then the marginal product of the 6th worker is

a.152 units of output.
b.55 units of output.
c.1 unit of output.
d.65 units of output.