You can always read your data into an array which then you can randomly access:

open(my $INFILE, ...) or die "unable to open file: $!\n";
chomp(my @lines = <$INFILE>);
close($INFILE);
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Now your lines are available as $lines[0] through $lines[$#lines], i.e.:

print "Number of lines read: ", 1+$#lines, "\n";
for my $i (0..$#lines) {
  print "line $i is: $lines[$i]\n";
}
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Since this looks like a homework problem, I'll leave it to you to figure the rest out.

Update: Fixed bad chomp usage.