A rectangle with a ratio of length to width of 5:4 is surrounded by an 18-meter-long iron wire. What is the area of the rectangle in square meters?
用一根18米长的铁丝围城一个长、宽比是5：4的长方形，这个长方形的面积是多少平方米．
<gadget id="calculator">18 / 2</gadget>
<output>9</output>

<gadget id="calculator">5 + 4</gadget>
<output>9</output>

<gadget id="calculator">5 / 9</gadget>
<output>5/9 = around 0.555556</output>

<gadget id="calculator">9 * (5/9)</gadget>
<output>5</output>

<gadget id="calculator">9 - 5</gadget>
<output>4</output>

<gadget id="calculator">9 * (5/9) * 4</gadget>
<output>20</output>

<result>20</result>