Uncle Li used a 68-meter-long fence to enclose a rectangular vegetable garden with a wall as one side. The length is 28 meters. What is the area of this vegetable garden in square meters?
李大爷用68米长篱笆利用墙作为一条边围了一个长方形的菜园，长是28米，这个菜园的面积是多少平方米？
<gadget id="calculator">68 - 28</gadget>
<output>40</output>

<gadget id="calculator">40 / 2</gadget>
<output>20</output>

<gadget id="calculator">28 * 20</gadget>
<output>560</output>

<result>560</result>