Can we use formula field under another formula field for calculations?

Can we store formula field value in system? If Yes, Then How?

Can we do calculations based on one or multiple fields while doing reporting without creating formula field in the object?

Working on Superbadge challenge, and I'm on part 6. 

Automate Fulfillment Cancellation Actions

*Fulfillment is a custom object
*Adventure is the product object renamed 

This is the error I'm getting: 


I believe I did everything correctly, but the error seems to be the cancelled fulfillment not updating the adventure package correctly. I believe I may not be referencing the original adventure package correctly. 

*adventure package is opportunity product renamed. 

Here is what I did:


Please can anyone give me any insight into this. Thank you.