Since I'm not the OP, it's unlikely I'm looking to get my homework solved. But then, it's unlikely any teacher would give the OP's problem as homework.
Thanks for the sample code, but I already know how to use Parallel::ForkManager, I've done so many times.
What I was seeking is an example of using that module to solve the OPs particular problem. You see, I cannot work out how it would pass back the result and carry from adding the first, rightmost, two digits back to the parent process so that the carry can be passed to the next child when adding the next two digits? Any thoughts?