If the length of a rectangle is 9 decimeters and its length is 4 decimeters, what is its area?
一个长方形的长是9分米，比宽长4分米，它的面积是多少．
<gadget id="calculator">9 - 4</gadget>
<output>5</output>

<gadget id="calculator">9 * 5</gadget>
<output>45</output>

<result>45</result>