Basic idea:

1. read in two-line chunks (read one line, then another)
2. Join the lines.
3. Strip out the leading zero, and any excess whitespace (including newlines).

open FILE, "file.txt" or die "Can't open file.txt:$!\n";

while(my $firstline = <FILE>) {
   $secondline = <FILE> or die "Ran out of lines!\n";
   # how to join the lines is left as an exercise for the
   # reader: hint ... Dot knows much.
}
[download]

For the second part, you can use a regular expression. Here's a hint: /^a/ matches an a at the beginning of a string. Here's another hint: \s{7,} matches seven whitespace (space, tab, newline) characters. The general syntax for a search-and-replace (substitution) pattern match is $string =~ s/tick/arthur/;, and the /g modifier on the end of a regular expression tells the system to perform each match it finds (instead of just the first).

The rest is left as an exercise for the reader. Study materials: perlre, perlretut.

HTH

Update theorbtwo pointed out I hadn't closed my ordered list tag.

If not P, what? Q maybe?
"Sidney Morgenbesser"