There are 192 cars at station A, and 48 cars at station B. There are 21 cars driving from station A to station B every day, and 24 cars driving from station B to station A. After how many days, the number of cars at station A will be B station 7 times.
甲站有汽车192辆，乙站有汽车48辆，每天从甲站开往乙站的汽车有21辆，从乙站开往甲站的汽车有24辆，多少天以后，甲站的汽车是乙站7倍．
<gadget id="calculator">192 + 48</gadget>
<output>240</output>

<gadget id="calculator">7 + 1</gadget>
<output>8</output>

<gadget id="calculator">240 / 8</gadget>
<output>30</output>

<gadget id="calculator">48 - 30</gadget>
<output>18</output>

<gadget id="calculator">24 - 21</gadget>
<output>3</output>

<gadget id="calculator">18 / 3</gadget>
<output>6</output>

<result>6</result>