The area of a trapezoid is 16cm**2, the upper base is 3cm, the height is 4cm, and the lower base is cm.
一个梯形的面积是16cm**2，上底是3cm，高是4cm，下底是多少cm．
<gadget id="calculator">4 / 2</gadget>
<output>2</output>

<gadget id="calculator">3 * 2</gadget>
<output>6</output>

<gadget id="calculator">16 - 6</gadget>
<output>10</output>

<gadget id="calculator">10 / 2</gadget>
<output>5</output>

<result>5</result>