The upper base of a trapezoid is 12m. The lower bottom is 21m. The height is 5m. What is the area of this trapezoid.
一个梯形的上底是12m．下底是21m．高是5m．这个梯形的面积是多少．
<gadget id="calculator">12 + 21</gadget>
<output>33</output>

<gadget id="calculator">5 / 2</gadget>
<output>5/2 = around 2.5</output>

<gadget id="calculator">33 * (5/2)</gadget>
<output>165/2 = around 82.5</output>

<result>165/2 = around 82.5</result>