Two cars, fast and slow, drive from place A to place B at the same time. The fast car travels 18 kilometers more than the slow car per hour. After driving for 4 hours to reach place B, the fast car returns to place A immediately, and is 42 kilometers away from place B. Slow trains meet, find the distance between A and B.
快、慢两辆汽车同时从甲地开往乙地，快车每小时比慢车多行18千米，快车行驶4小时到达乙地后，立即返回甲地，在离乙地42千米的地方与慢车相遇，求甲、乙两地距离．
<gadget id="calculator">18 * 4</gadget>
<output>72</output>

<gadget id="calculator">7 - 5</gadget>
<output>2</output>

<gadget id="calculator">72 / 2</gadget>
<output>36</output>

<gadget id="calculator">36 * 7</gadget>
<output>252</output>

<result>252</result>