The upper base of a trapezoid is 12dm, the height is 8dm, and the area is 108dm**2. How many decimeters is the lower base of this trapezoid?
一个梯形的上底是12dm，高是8dm，面积是108dm**2，这个梯形的下底是多少分米？
<gadget id="calculator">2 / 8</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">108 * (1/4)</gadget>
<output>27</output>

<gadget id="calculator">27 - 12</gadget>
<output>15</output>

<result>15</result>