The upper base of a trapezoid is 9cm, the lower base is 5cm, and the height is 4cm. What is its area in cm**2.
一个梯形的上底是9cm，下底是5cm，高是4cm，它的面积是多少cm**2．
<gadget id="calculator">9 + 5</gadget>
<output>14</output>

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

<gadget id="calculator">14 * 2</gadget>
<output>28</output>

<result>28</result>