There is a trapezoid, the sum of the upper and lower bases is 14 cm, and the height is 4 cm, what is the area of the trapezoid in square centimeters?
有一个梯形，上下底之和是14厘米，高4厘米，这个梯形的面积是多少平方厘米．
<gadget id="calculator">4 / 2</gadget>
<output>2</output>

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

<result>28</result>