data ia.percent2 ;
   if _n_ = 1 then do until (Last);
      set ia.monthsum(keep = RevCargo) end = Last;
      TotalRev + RevCargo;
   end;
   set ia.monthsum (keep = SaleMon RevCargo );
   PctRev = RevCargo / TotalRev;
run;

proc print data = ia.percent2(drop=TotalRev);
   title 'Creating Summary Statistics and Percentages';
   title2 'In the DATA Step';
run;