Question: How big should the entire shelf unit be when making easy cardboard shelves?

  Options: 
 A. Each unit should be built at most 2 inches wide. The height can vary somewhat depending on your needs, but 42 inches high makes the it stable and sturdy.
 B. Each unit should be built at most 20 inches wide. The height can vary somewhat depending on your needs, but 42 inches high makes the it stable and sturdy.
Answer: B