The Capital Stock Is Fixed at 5 Units,the Price of Capital

Multiple Choice

The capital stock is fixed at 5 units,the price of capital is $60 per unit,and the price of labor is $20 per unit. $$\begin{array} { c c } \text { Units of } & \text { Units of } \\\text { Labor } & \text { Output } \\\hline 2 & 10 \\4 & 26 \\6 & 46 \\8 & 60 \\10 & 72 \\12 & 80\end{array}$$ Based on the above,how much does the 12th unit of output add to the firm's total variable cost?

A) $2.50
B) $4
C) $5
D) $20
E) $40