I have to use process of elimination here because as much as Lord Byron is a wonderful wordsmith, Don Juan can be so very confusing to me at times. No matter, here we go:
The Peter Bell The Third quote is "criticises the subject for having abundant knowledge of the world but low self-awareness". A few clues; "all things he seemed to understand" and then "but his own mind... was a mist".
The first Don Juan quote is "criticises the subject for confusing his audience". This one was harder, but the clues here are: "I wish he would explain his explanation". This seems to suggest the audience is confused.
That leaves the final Don Juan quote in the middle to be "criticises his subject for his half baked knowledge".
Hope that I could help!
Answer:
I would say "Twenty dollars a week doesn’t go far. Expenses had been greater than she had calculated. They always are."
Explanation:
In this answer, it explicitly says " Expenses had been greater than she had calculated. They always are." which infers that by saying "they always are", would imply she never makes enough money to be financially fit.