设相遇时甲行驶的路程是 6x,则乙行驶的路程是 5x .两地相距s km.
有两种情况：
(1) 距离b还有15km.
s = 6x + 5x
s = 6x + 15
5x = 15
x = 3
s = 11x = 33 千米.
(2) 距离a还有15km.
s = 6x + 5x
s = 5x + 15
6x = 15
x = 2.5
s = 11x = 27.5 千米.
因为你题目中没说明是距离哪一端还有 15km 我都知道了！谢谢！