What is the area of a square board with a perimeter of 28 decimeters?
一块正方形木板，周长是28分米，它的面积是多少．
<gadget id="calculator">28 / 4</gadget>
<output>7</output>

<gadget id="calculator">7 * 7</gadget>
<output>49</output>

<result>49</result>