Just off the top of my head, here's some untested code that should get you started down the right path.

while ($Input = <IN>) {
  if ($Input !~ /^Answer/) {
     if ($Input =~ /^(\d+)/) {
        $Number = $1;
     }
     print QUESTION "$Input";
  }
  else {
     print ANSWER "$Number $Input";
  }
}
[download]

If things get any worse, I'll have to ask you to stop helping me.