my @nums = qw/ 3 9 2 9 /;;
{
  my $re = join '|', map { "\Q$_\E" } @nums;
  my $str = 'and a 3  9 2 9 ';
  $str =~ s{($re)}{"$1"}g;
  print "$str\n";
}

{
  my $re = join '\s*', map { "\Q$_\E" } @nums;
  my $str = 'and a 3  9 2 9 ';
  $str =~ s{($re)}{"$1"}g;
  print "$str\n";
}

__END__
and a "3"  "9" "2" "9" 
and a "3  9 2 9"