Teacher Xu crosses the river with two students (all three of them can row). Teacher Xu weighs 70 kg, and each student weighs 35 kg. There is only one small boat by the river. The small boat can carry up to 80 kilograms each time. It takes 12 minutes to cross the river. How many minutes will it take them all to cross the river?
许老师和两个学生过河(三人都会划船)，许老师体重70千克，每位学生体重35千克．河边只有一条小船，小船每次最多能载80千克，过河一程需12分钟，他们要多少分钟才能全部过河．
<gadget id="calculator">12 * 5</gadget>
<output>60</output>

<result>60</result>