perl -wMstrict -le
"my @ranges = qw(15 28-31 3-4 40 17-19  99- -99 -99- x x-x);
 my ($total_min, $total_max);
 ;;
 my $extract_ranges = qr{ \A (\d+) (?: - (\d+))? \z }xms;
 for (@ranges) {
   $total_min += /$extract_ranges/ && $1;
   $total_max += /$extract_ranges/ && $^N;
   }
 ;;
 print qq{total between $total_min and $total_max};
"
total between 103 and 109