Aunt Li surrounded a trapezoidal vegetable field with a wall in the yard. She shared a 29-meter-long fence. It is known that the wall is 6 meters long, the two waists of the trapezoid are 7 meters and 4 meters long, and the height is 3 meters. What is the area of the vegetable plot?
李阿姨在院子里靠一堵墙围了一块梯形的菜地，共用了29米长的篱笆，已知墙长6米，梯形两腰长分别为7米和4米，高为3米，这块菜地的面积是多少？
<gadget id="calculator">29 - 7 - 4</gadget>
<output>18</output>

<gadget id="calculator">3 / 2</gadget>
<output>3/2 = around 1.5</output>

<gadget id="calculator">18 * (3/2)</gadget>
<output>27</output>

<result>27</result>