A trapezoid has an area of 30 square meters, a height of 6 meters and an upper base of 4 meters. What is the length of the bottom of this trapezoid?
一个梯形的面积是30平方米，高6米，上底长4米．求这个梯形的下底的长多少？
<gadget id="calculator">2 / 6</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">30 * (1/3)</gadget>
<output>10</output>

<gadget id="calculator">10 - 4</gadget>
<output>6</output>

<result>6</result>