A trapezoid is composed of triangles and parallelograms with the same base and height. The area of the triangle is 6 square centimeters. How many square centimeters is the area of the trapezoid?
一个梯形是由等底等高的三角形和平行四边形组成的，三角形的面积是6平方厘米，梯形的面积是多少平方厘米？
<gadget id="calculator">6 * 2</gadget>
<output>12</output>

<gadget id="calculator">6 + 12</gadget>
<output>18</output>

<result>18</result>