Two people practice running at the same starting point, A runs 7 meters per second, and B runs 8 meters per second. If A runs for 3 seconds first, can B catch up with A after a few seconds?
两人在同一起点练习赛跑，甲每秒跑7米，乙每秒跑8米．如果甲先跑3秒，几秒钟后乙可追上甲？
<gadget id="calculator">8 - 7</gadget>
<output>1</output>

<gadget id="calculator">3 / 1</gadget>
<output>3</output>

<gadget id="calculator">7 * 3</gadget>
<output>21</output>

<result>21</result>