What is the area of a rectangle whose perimeter is 28 cm and whose length is 10 cm?
周长是28厘米的长方形，长是10厘米，面积是多少．
<gadget id="calculator">28 / 2</gadget>
<output>14</output>

<gadget id="calculator">14 - 10</gadget>
<output>4</output>

<gadget id="calculator">10 * 4</gadget>
<output>40</output>

<result>40</result>