A walks to a certain place at a speed of 8 kilometers per hour. B rides a bicycle to chase A from the same place 4 hours later than A. B travels 12 kilometers per hour. How long does it take for B to catch up with A?
甲以每小时8千米的速度步行去某地，乙比甲晚4小时骑自行车从同一地点出发追甲，乙每小时行12千米，乙几小时追上甲？
<gadget id="calculator">12 - 8</gadget>
<output>4</output>

<gadget id="calculator">4 / 4</gadget>
<output>1</output>

<gadget id="calculator">8 * 1</gadget>
<output>8</output>

<result>8</result>