One side of a square is reduced by 6 decimeters, and the other side is reduced by 10 decimeters to form a rectangle. The area of this rectangle is 260 square decimeters less than that of the square. Find the side length of the original square.
一个正方形一条边减少6分米，另一条边减少10分米后变成一个长方形，这个长方形的面积比正方形的面积少260平方分米，求原来的正方形的边长．
<gadget id="calculator">6 * 10</gadget>
<output>60</output>

<gadget id="calculator">60 + 260</gadget>
<output>320</output>

<gadget id="calculator">6 + 10</gadget>
<output>16</output>

<gadget id="calculator">320 / 16</gadget>
<output>20</output>

<result>20</result>