>perl -wMstrict -le
"my @ranges = ('15', '28-31', '3-4', '40', '17-19');
 my ($total_min, $total_max);
 ;;
 m{ \A       (\d+)   (?{ $total_min += $^N })
       (?: - (\d+))? (?{ $total_max += $^N })
    \z
  }xmsg for @ranges;
 ;;
 print qq{total between $total_min and $total_max};
"
total between 103 and 109