Formaula needed to Calculate orevious month revenue by name and date range

In which case try:

=SUMIFS($J$2:$J$82,$M$2:$M$82,"Accepted",$N$2:$N$82,">=09/01/15",$N$2:$N$82,"<=09/30/15",$R$2:$R$82,"Katrina Taylor")

and adjust the range according to the number of rows you have... I've restricted it to Rows 2 to 82 because this is the limit of the data in your sheet and because you have totals at the bottom of column J.

Let me know if that works for you?