=if(l6="a",if(countif($l$6:$l6,"a*")>countif($l$6:$l$25,"a*")*0.3,"b+",l6),if(l6="a+",if(countif($l$6:$l6,"a*")>countif($l$6:$l$25,"a*")*0.3,"b+",l6),l6))