The upper base of a trapezoid is 5 decimeters, the lower base is 7 decimeters, and the height is 4 decimeters. What is its area?
一个梯形上底是5分米，下底是7分米，高是4分米，它的面积是多少平方分米．
<gadget id="calculator">5 + 7</gadget>
<output>12</output>

<gadget id="calculator">4 / 2</gadget>
<output>2</output>

<gadget id="calculator">12 * 2</gadget>
<output>24</output>

<result>24</result>