Refer to the Following:
the Amount of Total Output Produced

Multiple Choice

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

$\begin{array}{cccc} &\text { Units of Capital }\\&& 1 & 2 & 3&4 \\\hline &1 & 50&120&160&180 \\\text {Units }&2 & 110&260&360&390 \\\text {of }&3 & 150&360&510&560\\\text {Labor }&4 & 170&430&630&690 \\&5 & 160&4801&710&790 \\\end{array}$
-If the capital stock is fixed at one unit, how much does the third unit of labor add to total output?

A) 20
B) 40
C) 60
D) 80
E) none of the above