foreach $filiais (@filiais){
  # print an html header (you don't need $cnt2 for this)
  $tf = $trf = $tm = $trm = 0; # set accumulators to 0
  foreach $month (1 .. 12) {
    # query DB for rows of 4 values _for_this_month_
    while (@rown = $sthn->fetchrow_array()) {
       ($fa,$rfa,$ma,$rma) = @rown;
       $tf += $fa;  # and likewise for the other three accumulators
    }
    if ( $month % 3 == 0 ) { # true for months 3,6,9,12
      ListTrimestre( $tf,$trf,$tm,$trm,$month/3 );
      $tf = $trf = $tm = $trm = 0; # reset accumulators to 0
    }
  }
}