A square, after increasing the side length by 3 meters, the area increases by 81 square meters, what is the area of the original square?
一块正方形，边长增加3米后，面积增加81平方米，原来正方形的面积是多少？
<gadget id="calculator">3 * 3</gadget>
<output>9</output>

<gadget id="calculator">81 - 9</gadget>
<output>72</output>

<gadget id="calculator">72 / 3 / 2</gadget>
<output>12</output>

<gadget id="calculator">12 * 12</gadget>
<output>144</output>

<result>144</result>