A rectangle, the ratio of length to width is 7:3, if the length is reduced by 12 decimeters, it becomes a square. What is the area of the original rectangle?
一个长方形，长与宽的比是7：3，若把长减少12分米，就变成正方形．原来长方形的面积是多少平方分米？
<gadget id="calculator">7 - 3</gadget>
<output>4</output>

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

<gadget id="calculator">7 * 3</gadget>
<output>21</output>

<gadget id="calculator">3 * 3</gadget>
<output>9</output>

<gadget id="calculator">21 * 9</gadget>
<output>189</output>

<result>189</result>