The area of a parallelogram formed by two identical trapezoids is 80 square centimeters, the height is 5 centimeters, the upper base of the trapezoid is 7 cm, and the lower base of the trapezoid is how many centimeters.
两个完全一样的梯形拼成的一个平行四边形的面积是80平方厘米，高是5厘米，梯形的上底是7厘米，梯形的下底是多少厘米．
<gadget id="calculator">80 / 2</gadget>
<output>40</output>

<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">40 * (2/5)</gadget>
<output>16</output>

<gadget id="calculator">16 - 7</gadget>
<output>9</output>

<result>9</result>