trapezoid has two angles that are right angles, and the length of the sum of the upper and lower bases and the shorter waist is 20 cm. What is the area of the trapezoid in square centimeters?
一个梯形有两个角是直角，并且上、下底的和与较短的腰的长度都是20厘米，这个梯形的面积是多少平方厘米．
<gadget id="calculator">20 / 2</gadget>
<output>10</output>

<gadget id="calculator">20 * 10</gadget>
<output>200</output>

<result>200</result>