The perimeter of a rectangle is 30 meters and the length is 8 meters. What is its area in m**2.
一个长方形的周长是30米，长是8米，它的面积是多少m**2．
<gadget id="calculator">30 / 2</gadget>
<output>15</output>

<gadget id="calculator">15 - 8</gadget>
<output>7</output>

<gadget id="calculator">8 * 7</gadget>
<output>56</output>

<result>56</result>