The upper base of a trapezoid is 3 meters, the lower base is 6 meters, and the height is 4 meters. What is the area of the trapezoid in square meters?
一个梯形的上底是3米，下底是6米，高是4米，这个梯形的面积是多少平方米．
<gadget id="calculator">3 + 6</gadget>
<output>9</output>

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

<gadget id="calculator">9 * 2</gadget>
<output>18</output>

<result>18</result>