9 children stand in a circle and play games, with a distance of 2 meters between them. Do you know how many meters there are in this circle?
9个小朋友站成一圈做游戏，每两人之间相隔2米，你知道这一圈共多少米吗？
<gadget id="calculator">2 * 9</gadget>
<output>18</output>

<result>18</result>