person goes from place A to place B and returns to place A. He walks a kilometer more than the day before. As a result, it takes 5 days to go and 4 days to return. What is the distance between places A and B in kilometers? ．
某人从甲地去乙地再返回甲地，他每天比前一天多走a千米，结果去时用5天，回来时用了4天，那么甲、乙两地的距离是多少千米．
<result>90</result>