假令A、B间的距离为S.
则有:
S/(7.5+2.5)+(S-15)/(7.5-2.5)=9.
S/10+(S-15)/5=9
(S+2S-30)/10=9
3S-30=90
3S=120
S=40.
即:A.B间距离为40KM.