It is known that the No. 4 bus departs once every 10 minutes, and the No. 6 bus departs once every 15 minutes. After leaving one at the same time, it will depart at the same time at least ___ minutes later. How many
已知4路公共汽车10分钟开出一辆，6路公共汽车15分钟开出一辆，同时开出一辆后，至少再过___分钟又同时开出．多少
<result>30</result>