The sum of the upper and lower bases of a trapezoid is 10 decimeters, and the height is 4 decimeters. What is the area in square decimeters?
一个梯形的上下底之和是10分米，高是4分米，面积是多少平方分米．
<gadget id="calculator">4 / 2</gadget>
<output>2</output>

<gadget id="calculator">10 * 2</gadget>
<output>20</output>

<result>20</result>