There is a square vegetable field, and the length of the surrounding fence is 36 meters. What is the area of this vegetable field?
有一块正方形的菜地，周围篱笆的长度是36米，这块菜地的面积是多少．
<gadget id="calculator">36 / 4</gadget>
<output>9</output>

<gadget id="calculator">9 * 9</gadget>
<output>81</output>

<result>81</result>