and B start from the starting point at the same time and walk in the same direction. A travels 5 kilometers per hour, while B travels 1 kilometer in the first hour and 2 kilometers in the second hour. Each subsequent hour is faster than the previous hour. More than 1 km. Question: How many hours did it take for B to catch up with A?
甲、乙二人同时从起点出发，向同一方向行走，甲每小时行5千米，而乙第一小时行1千米，第二小时行2千米，以后每行1小时比前一小时多行1千米．问：经过多少小时乙追上甲？
<gadget id="calculator">10 - 1</gadget>
<output>9</output>

<result>9</result>