For a rectangular experimental field, no matter if the length is increased by 4 meters or the width is increased by 2 meters, the area will increase by 12 square meters compared with the original one. What is the area of the original test field in square meters?
一块长方形试验田，无论长增加4米，或宽增加2米，面积都比原来增加12平方米．原来试验田的面积是多少平方米？
<gadget id="calculator">12 / 2</gadget>
<output>6</output>

<gadget id="calculator">12 / 4</gadget>
<output>3</output>

<gadget id="calculator">6 * 3</gadget>
<output>18</output>

<result>18</result>