A square vegetable field has a perimeter of 28 decimeters. What is the area of this vegetable field?
一个正方形菜地，它的周长是28分米，问这块菜地的面积是多大？
<gadget id="calculator">28 / 4</gadget>
<output>7</output>

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

<result>49</result>