Two cars drive from A and B oppositely at the same time, and meet at a distance of 18 kilometers from the midpoint 3 hours later. It is known that the speed of the slow train is that of the fast train (5/7), how many kilometers are the distance between A and B?
两辆汽车同时从A、B两地相对开出，3小时后在距中点18千米处相遇．已知慢车的速度是快车的(5/7)，A、B两地相距多少千米．
<gadget id="calculator">7 + 5</gadget>
<output>12</output>

<gadget id="calculator">7 / 12</gadget>
<output>7/12 = around 0.583333</output>

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

<gadget id="calculator">(7/12) - (1/2)</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">18 / (1/12)</gadget>
<output>216</output>

<result>216</result>