Two athletes, A and B, are running a race. A runs 7 meters per second, and B runs 6.5 meters per second. If B is allowed to run 15 meters first, and A starts to catch up, how many seconds will A catch up with B?
甲、乙两个运动员赛跑，甲每秒跑7米，乙每秒跑6.5米，如果让乙先跑出15米，甲再开始追，几秒钟后甲追上乙？
<gadget id="calculator">7 - 6.5</gadget>
<output>0.5</output>

<gadget id="calculator">15 / 0.5</gadget>
<output>30</output>

<result>30</result>