An experiment conducted in Tennessee found that the scores of second graders and third graders on standardized tests for reading, math, listening, and word study skills were the same in small classrooms (13 to 17 students) as in regular classrooms (22 to 25 students). Suppose that there is a school that had 90 third graders taught by four teachers that added two additional teachers to reduce class sizes. If the Tennessee study can be generalized, what is the marginal product of labor (MP_L) of these two additional teachers?