The ratio of length to width of a rectangle is 5:3. If the width is increased by 12 cm, the rectangle becomes a square. What is the area of the original rectangle?
一个长方形的长和宽的比是5：3，如果宽增加12厘米，则长方形变成正方形，原来长方形的面积是多少平方厘米？
<gadget id="calculator">5 - 3</gadget>
<output>2</output>

<gadget id="calculator">12 / 2</gadget>
<output>6</output>

<gadget id="calculator">5 * 6</gadget>
<output>30</output>

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

<gadget id="calculator">30 * 18</gadget>
<output>540</output>

<result>540</result>