The area of a trapezoid is 80 square meters, the height is 5 meters, the length of the upper base is 15 meters, what is the length of the lower base?
一个梯形的面积是80平方米，高5米，上底长15米，下底长是多少．
<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">80 * (2/5)</gadget>
<output>32</output>

<gadget id="calculator">32 - 15</gadget>
<output>17</output>

<result>17</result>