A trapezoid has an area of 80 square centimeters, its upper base is 9 cm, and its height is 5 cm. Find its lower base. (solution by equation)
一个梯形，面积是80平方厘米，它的上底是9厘米，高是5厘米，求它的下底．(用方程解)
<gadget id="calculator">5 / 2</gadget>
<output>5/2 = around 2.5</output>

<gadget id="calculator">9 * (5/2)</gadget>
<output>45/2 = around 22.5</output>

<gadget id="calculator">80 - (45/2)</gadget>
<output>115/2 = around 57.5</output>

<gadget id="calculator">(115/2) / (5/2)</gadget>
<output>23</output>

<result>23</result>