The area of an isosceles trapezoid is 20 square meters, the height is 4 meters, the lower base is 3 meters, what is the upper base?
一个等腰梯形的面积是20平方米，高是4米，下底是3米，上底是多少．
<gadget id="calculator">2 / 4</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">20 * (1/2)</gadget>
<output>10</output>

<gadget id="calculator">10 - 3</gadget>
<output>7</output>

<result>7</result>