EDIT: I came to A solution, but I am afraid it is not winning beauty contests…
Still interested in answers to my questions
I got the Portfolio challenge working to and up the list of 10 stock items, but I can’t get the sum method (shown in Employees example code, there: valueOfAssets:) working. I need that to get the total value of the Portfolio.
I really want to find the solution myself, but I really need some help. May I please ask some questions without posting my code, because, again, I want to find the solution myself.
So.

I did not make Portfolio and Stockholding inherit from each other, but both subclasses of NSObject. Is that correct?
(I did not forget to import in each other, and in main.m); 
I suppose that I don’t need the method ‘AddAssetsObject’, as shown in the Employees example. I thought it is redundant in the Portfolio challenge. Am I wrong? Do I need it to get the summethod working?

I created only one array, NSMutableArray *portfolio. One solution I think of: maybe I need a second array.
Your comments will be appreciated…