There are two paper tapes, one is 21 cm long and the other is 13 cm long. After cutting the two paper tapes to the same length, it is found that the remaining length of the short paper tape is the rest of the long paper tape (8/13 ), how many centimeters is the cut section?
有两条纸带，一条长21厘米，另一天长13厘米，把两条纸带都剪下同样长的一段后，发现短纸带剩下的长度是长纸带剩下的(8/13)，剪下的一段有多少厘米？
<gadget id="calculator">8 / 13</gadget>
<output>8/13 = around 0.615385</output>

<gadget id="calculator">(8/13) * 21</gadget>
<output>168/13 = around 12.923077</output>

<gadget id="calculator">13 - (168/13)</gadget>
<output>1/13 = around 0.076923</output>

<gadget id="calculator">1 - (8/13)</gadget>
<output>5/13 = around 0.384615</output>

<gadget id="calculator">(1/13) / (5/13)</gadget>
<output>1/5 = around 0.2</output>

<result>1/5 = around 0.2</result>