The area of a trapezoid is 30 square meters, the upper base is 6 meters, the height is 4 meters, and the lower base is how many meters.
一个梯形面积是30平方米，上底6米，高4米，下底多少米．
<gadget id="calculator">2 / 4</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">30 * (1/2)</gadget>
<output>15</output>

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

<result>9</result>