A trapezoid has an upper base of 5 cm, a lower base of 7 cm, and a height of 4 cm. What is the area of the trapezoid in square centimeters?
一个梯形，它的上底是5厘米，下底是7厘米，高是4厘米，这个梯形的面积是多少平方厘米．
<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>