There are 21 workers in the workshop producing bolts and nuts. Each person produces an average of 12 bolts or 18 nuts per day. There are currently several workers producing bolts and other workers producing nuts. It happens that the bolts and nuts produced every day are matched at a ratio of 1:2. Number of workers producing nuts.
车间有21名工人生产螺栓和螺母，每人每天平均生产螺栓12个或螺母18个，现有若干名工人生产螺栓，其他工人生产螺母，恰好每天生产的螺栓和螺母按1：2配套，求生产螺母的工人人数．
<gadget id="calculator">12 * 21</gadget>
<output>252</output>

<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">(1/2) * 18</gadget>
<output>9</output>

<gadget id="calculator">12 + 9</gadget>
<output>21</output>

<gadget id="calculator">252 / 21</gadget>
<output>12</output>

<result>12</result>