Robert Penn Warren books in order
6 books in the catalogue, about 82 hours of reading in all; the shortest takes 10 hours and the longest 23 hours.
6 standalone books in the catalogue.
Standalone books
Understanding Poetry 10.9 h 
Understanding Fiction 11.2 h 
All the King's Men 9.5 h 
The United States in Literature [with Three Long Stories] -- Seventh Edition 15.0 h 
Understanding Fiction -- Second Edition 12.6 h 
Prentice Hall Literature--Timeless Voices, Timeless Themes--The American Experience 22.5 h