The area of a trapezoid is 24 square centimeters, the length of the lower base is 7 cm, the height is 4 cm, what is the upper base in cm?
一个梯形的面积是24平方厘米，下底长7厘米，高是4厘米，上底是多少厘米．
<gadget id="calculator">2 / 4</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">24 * (1/2)</gadget>
<output>12</output>

<gadget id="calculator">12 - 7</gadget>
<output>5</output>

<result>5</result>