A rectangular piece of land has a ratio of length to width of 3:1. If the length of the rectangular land is increased by 1 meter, the area of the rectangular land obtained by increasing the width by 1 meter is exactly 10 square meters less. So, how many square meters is the original rectangular land?
一块长方形土地，长和宽的比为3：1．如果将长增加1米后的长方形土地，比将宽增加1米后的长方形土地面积刚好少了10平方米．那么，原来的长方形土地有多少平方米？
<gadget id="calculator">3 - 3 - 1</gadget>
<output>-1</output>

<gadget id="calculator">3 + (-1)</gadget>
<output>2</output>

<gadget id="calculator">10 / 2</gadget>
<output>5</output>

<gadget id="calculator">5 * 3 * 5</gadget>
<output>75</output>

<result>75</result>