A rectangular iron plate, the width is the length (4/5). After cutting off 21 cm from the wide side and 35% from the long side, a square iron plate is obtained. What is the length of the original rectangular iron plate in centimeters?
一块长方形铁板，宽是长的(4/5)．从宽边截去21厘米，长边截去35%以后，得到一块正方形铁板．问原来长方形铁板的长是多少厘米．
<gadget id="calculator">35 / 100</gadget>
<output>7/20 = around 0.35</output>

<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">(4/5) - 1</gadget>
<output>-1/5 = around -0.2</output>

<gadget id="calculator">(7/20) + (-1/5)</gadget>
<output>3/20 = around 0.15</output>

<gadget id="calculator">21 / (3/20)</gadget>
<output>140</output>

<result>140</result>