piece of steel has a cross-section of a square with a side length of 1 decimeter. The surface area of this piece of steel is 42 square decimeters. What is its length?
一段钢材，横截面是边长1分米的正方形，这段钢材的表面积是42平方分米，它的长是多少．
<gadget id="calculator">1 * 1 * 2</gadget>
<output>2</output>

<gadget id="calculator">42 - 2</gadget>
<output>40</output>

<gadget id="calculator">1 * 4</gadget>
<output>4</output>

<gadget id="calculator">40 / 4</gadget>
<output>10</output>

<result>10</result>