There is a point O in the quadrilateral ABCD. The length of the perpendicular lines from the point O to the four sides is 2 cm. The perimeter of the quadrilateral ABCD is 18 cm. What is the area of the quadrilateral ABCD in square centimeters?
在四边形ABCD中有一点O，点O到四条边的垂线的长都是2厘米，四边形ABCD的周长是18厘米，则四边形ABCD的面积是多少平方厘米．
<gadget id="calculator">18 / 4</gadget>
<output>9/2 = around 4.5</output>

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

<gadget id="calculator">(9/2) * 4</gadget>
<output>18</output>

<result>18</result>