A long-distance bus station sends a bus to the north line every 20 minutes, and sends a bus to the south line every 15 minutes. If it sends a bus to the two lines at the same time, how many minutes have passed before the bus departs at the same time?
某长途汽车站向北线每20分钟发一辆汽车，向南线每15分钟发一辆汽车，如果同时向两线发车，至少经过多少分钟又同时发车？
<gadget id="calculator">2 * 2 * 3 * 5</gadget>
<output>60</output>

<result>60</result>