The elder sister has 640 yuan, and the younger sister has 310 yuan. From now on, the elder sister saves 20 yuan a day, and the younger sister saves 50 yuan a day. After a few days, the money of the two will be equal? how many days)
姐姐有640元，妹妹有310元，现在起姐姐每天存20元，妹妹每天存50元，几天后，两人的钱会相等？多少天)
<gadget id="calculator">640 - 310</gadget>
<output>330</output>

<gadget id="calculator">50 - 20</gadget>
<output>30</output>

<gadget id="calculator">330 / 30</gadget>
<output>11</output>

<result>11</result>