For two pieces of cloth of the same length, the first piece uses 23.9 meters, and the second piece uses 16.7 meters. As a result, the remaining meters of the second piece are 2.5 times that of the first piece. How many meters was the first piece of cloth?
两块同样长的布，第一块用去23.9米，第二块用去16.7米，结果第二块余下的米数是第一块的2.5倍．原来第一块布有多少米？
<gadget id="calculator">23.9 - 16.7</gadget>
<output>7.2</output>

<gadget id="calculator">2.5 - 1</gadget>
<output>1.5</output>

<gadget id="calculator">7.2 / 1.5</gadget>
<output>4.8</output>

<gadget id="calculator">4.8 + 23.9</gadget>
<output>28.7</output>

<result>28.7</result>