The upper base of a trapezoid is 5cm, the lower base is 7cm, and the height is 4cm. What is the area of the trapezoid in cm**2.
一个梯形的上底是5cm，下底是7cm，高是4cm，这个梯形的面积是多少cm**2．
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">5 + 7</gadget>
<output>12</output>

<gadget id="calculator">(1/2) * 12 * 4</gadget>
<output>24</output>

<result>24</result>