The area of a trapezoid is 1560 square meters, the upper base is 23 meters, and the height is 40 meters. How many meters is its lower base?
一个梯形面积是1560平方米，上底是23米，高是40米，它的下底是多少米？
<gadget id="calculator">2 / 40</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">1_560 * (1/20)</gadget>
<output>78</output>

<gadget id="calculator">78 - 23</gadget>
<output>55</output>

<result>55</result>