Hypothetical Production Schedule for a Two-Product Economy -If the Economy Is Producing at Point B,the Opportunity Cost

Hypothetical Production Schedule for a Two-Product Economy $\begin{array}{ccc}&Units~ of&Units~ of\\\text { Points } & \text { Consumer Goods } & \text { Capital Goods } \\\hline \mathrm{A} & 0 & 30 \\\mathrm{B} & 15 & 24 \\\mathrm{C} & 27 & 18 \\\mathrm{D} & 36 & 12 \\\mathrm{E} & 42 & 6 \\\mathrm{F} & 45 & 0\end{array}$
-If the economy is producing at point B,the opportunity cost of gaining 12 units of consumer goods is _______ units of capital goods.