A rope, three-eighths of its total length was used for the first time, and 15 meters was used for the second time. At this time, the ratio of what was cut to the rest was 7:5. How many meters was cut for the first time?
一根绳子，第一次用去了全长的八分之三，第二次用去了15米，这时剪去的与剩下的比是7：5，第一次剪去多少米？
<gadget id="calculator">7 + 5</gadget>
<output>12</output>

<gadget id="calculator">7 / 12</gadget>
<output>7/12 = around 0.583333</output>

<gadget id="calculator">3 / 8</gadget>
<output>3/8 = around 0.375</output>

<gadget id="calculator">(7/12) - (3/8)</gadget>
<output>5/24 = around 0.208333</output>

<gadget id="calculator">15 / (5/24)</gadget>
<output>72</output>

<gadget id="calculator">72 * (3/8)</gadget>
<output>27</output>

<result>27</result>