There is a tourist group of 40 people who came to a lake area for a tour, a total of 5.5km around the lake, a sightseeing bus can only drive around the lake in one direction, and can only carry 20 people at a time, and the speed when driving empty is 18km per hour , when fully loaded, the speed is 12km per hour, and the walking speed of people is 3km per hour. In order to tour for a week as soon as possible and return to the starting point at the same time, arrange half of the people to take the bus and the other half to walk. The passengers get off and walk on the way, and the tour bus continues How many minutes did it take to catch up with the walking tourists around the lake and bring them to the starting point?
有一个40人的旅游团来到了一个湖区游览，绕湖一周共5.5km，一辆观光游览车只能单方向绕湖行驶，且每次只能承载20人，空驶时的速度为每小时18km，满载时速度为每小时12km，人步行速度为每小时3km，为了尽快游览一周并同时回到起点，先安排一半人乘车，另一半步行，乘车人在途中下车步行，游览车继续绕湖追上步行游客，带上他们一直到起点，这个过程共用了多少分钟．
<result>50</result>