Xiaohong took out her own money (4/7), Xiaoli took out her own money (3/5), and each of them bought the same dictionary. Knowing that Xiaohong originally had 21 yuan, ask Xiaoli to use her original how much?
小红拿出自己钱的(4/7)，小丽拿出自己钱的(3/5)，两人各买一本同样的字典，已知小红原有21元，求小丽原有多少元？
<gadget id="calculator">4 / 7</gadget>
<output>4/7 = around 0.571429</output>

<gadget id="calculator">3 / 5</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">(4/7) / (3/5)</gadget>
<output>20/21 = around 0.952381</output>

<gadget id="calculator">21 * (20/21)</gadget>
<output>20</output>

<result>20</result>