There is a rectangular vegetable field. If the length is increased by 7 meters or the width is increased by 3 meters, the area will be increased by 42 square meters. What is the original area of this rectangular vegetable field in square meters?
有一块长方形菜地，如果长增加7米，或者宽增加3米，面积都比原来增加42平方米，这块长方形菜地原来面积是多少平方米．
<gadget id="calculator">42 / 3</gadget>
<output>14</output>

<gadget id="calculator">42 / 7</gadget>
<output>6</output>

<gadget id="calculator">14 * 6</gadget>
<output>84</output>

<result>84</result>