Xiaoli's bed is 20 decimeters long and 12 decimeters wide. Now to make a bed sheet, the bed sheet is required to hang down by 1 decimeter on both sides of the bed. What is the area of this bed sheet in square decimeters?
小丽的床长是20分米，宽是12分米．现在要做一个床单，要求床单在床的两侧各垂下1分米．这个床单的面积是多少平方分米？
<gadget id="calculator">12 + 1 + 1</gadget>
<output>14</output>

<gadget id="calculator">20 * 14</gadget>
<output>280</output>

<result>280</result>