Open Internet by MindsNet

Computer Science

I've spent hours trying to understand this part. Data Structures — Seymour Lipschutz. This question is from 4.24 of the book Data Structures by Seymour Lipschutz. I can't wrap my head around it, especially the part where we add E2 to E1L2 or where we add E3 in the last step. Kindly explain it for me.