The long-distance bus station sends a car to place A every 15 minutes, and sends a car to place B every 10 minutes. The two buses leave at 7:20 in the morning at the same time. How long does it take to leave at the same time?
长途汽车站每隔15分钟向A地发一辆车，每隔10分钟向B地发一辆车，这两趟车早上7：20同时发车，至少经过多长时间又同时发车？
<gadget id="calculator">3 * 5 * 2</gadget>
<output>30</output>

<result>30</result>