设：甲的速度为X,乙的速度为X-2
2X+（X-2）×2+36=4X+（X-2）×4-36
2X+2X-4+36=4X+4X-8-36
4X+32=8X-44
8X-4X=32+44
4X=76
X=19
19-2=17
19×2+17×2+36=108
答：甲的速度为19km/h,乙的速度为17km/h,;A.B两地的距离108km
108×2÷(17+19)=6