Two people, A and B, start from the two ends of the diameter of a circular field at the same time and move around the circular route at a constant speed in opposite directions. After B has walked 120 meters, they meet for the first time. They meet again at 40 meters, what is the circumference of this circular field?
甲和乙两人分别从一圆形场地的直径两端点同时开始以匀速按相反的方向绕此圆形路线运动，当乙走了120米以后，他们第一次相遇，在甲走完一周前40米处又第二次相遇，求此圆形场地的周长？
<gadget id="calculator">120 * 3</gadget>
<output>360</output>

<gadget id="calculator">360 - 40</gadget>
<output>320</output>

<gadget id="calculator">320 * 2</gadget>
<output>640</output>

<result>640</result>