The Table Below Shows the Total Production for Varying Numbers

The table below shows the total production for varying numbers of hours worked producing yo- yos.The firm sells its product and hires its workers in competitive markets. $$\begin{array} { | c | c | c | c | } \hline \begin{array} { c } \text { Number of } \\\text { Hours Worked }\end{array} & \begin{array} { c } \text { Number of } \\\text { Yo-Yos } \\\text { Produced }\end{array} & \begin{array} { c } \text { Wage Rate } \\\text { per Hour } ( \$ ) \end{array} & \begin{array} { c } \text { Price of Yo- Yos } \\( \$ ) \end{array} \\\hline 10 & 60 & 10 & 5 \\\hline 11 & 70 & 10 & 5 \\\hline 12 & 78 & 10 & 5 \\\hline 13 & 84 & 10 & 5 \\\hline 14 & 88 & 10 & 5 \\\hline 15 & 90 & 10 & 5 \\\hline\end{array}$$ TABLE 13- 4
-Refer to Table 13- 4.Which of the following statements best describes the situation of this firm when it is employing 12 hours of labour? The 12th hour of labour hired

A) adds $30 to revenue,but only costs $10 to hire,so this firm should hire more labour.
B) adds $8 to revenue,but costs $10 to hire,so this firm should hire less labour.
C) adds $5 to revenue,but costs $10 to hire,so this firm should hire less labour.
D) adds $10 to revenue and costs $10 to hire,so this firm is maximizing its profit at 12 hours of labour.
E) adds $40 to revenue,but only costs $10 to hire,so this firm should hire more labour.