Bus No. 4 departs every 9 minutes, and Bus No. 5 departs every 15 minutes. After the two buses depart at the same time, how many minutes must pass before the two buses depart at the same time for the second time?
4路公交车每隔9分钟发一次车，5路公交车每隔15分钟发一次车，这两路公交车同时发车以后，至少过多少分钟两路车才第二次同时发车？
<gadget id="calculator">3 * 3 * 5</gadget>
<output>45</output>

<result>45</result>