Put two equal squares together to form a rectangle. The perimeter of the rectangle is 21 decimeters. What is its area in square decimeters?
把两个相等的正方形拼成一个长方形，长方形的周长是21分米，它的面积是多少平方分米．
<gadget id="calculator">2 * 2</gadget>
<output>4</output>

<gadget id="calculator">2 + 4</gadget>
<output>6</output>

<gadget id="calculator">21 / 6</gadget>
<output>7/2 = around 3.5</output>

<gadget id="calculator">(7/2) * 2 * (7/2)</gadget>
<output>49/2 = around 24.5</output>

<result>49/2 = around 24.5</result>