The search query itself is a good starting point. Typing the exact phrase into a search engine can lead directly to a digital copy. Several of the top results for this search point to specific online sources:
In many standard printings of Princi i Vogel (e.g., by author or as used in Albanian technical schools), page 31 often falls within the early sections of Chapter 2 or Chapter 3 , focusing on: princi i vogel pdf 31