#wrap{width:970px; margin:0 auto;}

#mainbody{【任务3】 margin-top:15px;}

#left{float:left;width:110px; }

#mid{【任务2】width:650px;border:1px solid #999;}

#right{【任务3】border:1px solid #999;}

#wrap{width:970px; margin:0 auto;}

#mainbody{position:relative; margin-top:15px;}

#left{float:left;width:110px;border:1px solid #999;}

#mid{margin-left:124px;width:650px;border:1px solid #999;}/*0+2+0+109+13*/

#right{position:absolute;top:0px;margin-left:792px;border:1px solid #999;}/*124+2+0+649+17*/