The area of parallelogram ABCD is 30 square centimeters, E is a point on the extension line of side AD, EB and DC intersect at point F, if the area of △FBC is 9 square meters larger than the area of △FDE, and AD=5cm, then DE is equal to how many centimeters?
平行四边形ABCD的面积是30平方厘米，E为AD边延长线上的一点，EB与DC交于F点，如果△FBC的面积比△FDE的面积大9平方米，且AD=5厘米，那么DE等于多少厘米？
<gadget id="calculator">30 - 9</gadget>
<output>21</output>

<gadget id="calculator">30 / 5</gadget>
<output>6</output>

<gadget id="calculator">2 / 6</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">21 * (1/3)</gadget>
<output>7</output>

<gadget id="calculator">7 - 5</gadget>
<output>2</output>

<result>2</result>