A square plank is cut off by 8 cm on one side and 5 cm on the adjacent side. The remaining rectangular plank is 415 cm2 smaller than the original square. Find the side length of the original plank.
一块正方形木板，一边截去8厘米，邻边再截去5厘米，剩下的长方形木板比原来正方形小415平方厘米，求原来木板的边长．
<gadget id="calculator">8 * 5</gadget>
<output>40</output>

<gadget id="calculator">415 + 40</gadget>
<output>455</output>

<gadget id="calculator">5 + 8</gadget>
<output>13</output>

<gadget id="calculator">455 / 13</gadget>
<output>35</output>

<result>35</result>