G'day snackpie,

Welcome to the monastery.

There should sufficient information in (or linked from) "Perl introduction for beginners" to do this.

If you provide us with more information regarding what you're actually having difficulty with, we can no doubt provide more help. As it stands, without any code or other hints, I've no idea whether your issue is opening a file, reading a file, finding the line, doing the arithmetic, etc. The guidelines in "How do I post a question effectively?" exlpain what sort of information to provide such that we are better able to assist you.