A and B start from two places 15 kilometers apart at the same time and walk in the same direction. A travels 10 kilometers per hour, and B travels 7 kilometers per hour. How many hours can A catch up with B?
甲乙两人同时从相距15千米的两地动身，同向而行，甲每小时行10千米，乙每小时行7千米，甲在乙的后面多少小时可以追上乙？
<result>2</result>