Refer to the Following:
Amount of Total Output Produced from Various

Refer to the following:
Amount of total output produced from various combinations of labor and capital.

$\begin{array}{cccc} &\text { Units of Capital }\\&& 1 & 2 & 3 \\\hline &1 & 80 & 100 & 120 \\\text {Units }&2 & 180 & 220 & 260 \\\text {of }&3 & 270 & 330 & 390 \\\text {Labor }&4 & 340 & 420 & 500 \\&5 & 390 & 490 & 590 \\&6 & 410 & 530 & 650\end{array}$
-If capital is fixed at two units, what is the marginal product of the fourth unit of labor?

A) 60
B) 80
C) 100
D) 420
E) none of the above