A rectangle has a perimeter of 30 cm and a length of 9 cm. What is the area of the rectangle in square centimeters?
一个长方形，周长是30厘米，长是9厘米，这个长方形的面积是多少平方厘米．
<gadget id="calculator">30 / 2</gadget>
<output>15</output>

<gadget id="calculator">15 - 9</gadget>
<output>6</output>

<gadget id="calculator">9 * 6</gadget>
<output>54</output>

<result>54</result>