First, find out how long it takes my brother to get from school to the teaching building: 540÷60=9 (minutes), and then find out how far my sister has gone at this time, 9×48=432 (meters). It took nine minutes at this time, and then find out the time when my sister and brother met. At this time, my brother and sister are walking, the distance is 540-432, and the speed is the speed of my brother plus the speed of my sister. The time used is (540-432)÷(60+48)= 1 min, and the time used for * * is10+1=1(min). This is just an analysis. As for how to do it, I'll do it myself.