The area of a trapezoidal lawn is 30.4 square meters, the upper base is 6.3 meters, and the height is 4 meters. How long is its lower base?
一个梯形的草坪面积是30.4平方米，上底为6.3米，高为4米，它的下底长多少米？
<gadget id="calculator">2 / 4</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">30.4 * (1/2)</gadget>
<output>15.2</output>

<gadget id="calculator">15.2 - 6.3</gadget>
<output>8.9</output>

<result>8.9</result>