The Following Data Show the Total Output for a Firm

The following data show the total output for a firm when different amounts of labour are combined with a fixed amount of capital.Assume that the wage per unit of labour is $10 and the cost of the capital is $50. $$\begin{array} { | c | l | } \hline \text { Lab our per period } & \text { Total output per period } \\\hline 0 & 0 \\\hline 1 & 10 \\\hline 2 & 30 \\\hline 3 & 90 \\\hline 4 & 132 \\\hline 5 & 150 \\\hline\end{array}$$ TABLE 7- 3
-Refer to Table 7- 3.If this firm is producing 20 units of output per period its marginal cost is

A) 16.7 cents.
B) $10.00.
C) 50 cents.
D) $1.67.
E) $1.00.