To make a kind of parts, A makes one in 5 minutes, and B makes one in 15 minutes. Now to make 1080 such parts, how many hours will it take for A and B to make them at the same time?
要做一种零件，甲5分钟做一个，乙15分钟做一个．现在要做1080个这种零件，由甲乙同时做要用多少小时．
<result>67.5</result>