英语：We were told not to spend much time on playing by our teacher.
数学：设船在静水中的速度为v1,水的速度为v2
那么：140/（v1+v2)=7
140/ (v1-v2)=10
解方程组可得：v1=17km/h v2=3km/h
v1+v2为顺水速度；v1-v2为逆水速度