How does fitzgerald use sarasm and irony to convey his point of view about society during gatsbys

[What a fabulous question!  I really enjoyed thinking about this, . . . and it took me a long while to formulate my answer as a result!  I originally thought Tom would be the main culprit but then I couldn't think of a single example.  Honestly, I hope some other teacher figures out some further examples to add to the rich content here.  This being said, my answer follows.]

about the letter or who wrote the letter

type of error:

the error in the sentence is a "dangling modifier". a dangling modifier is a phrase, word or clause that "dangles" because there is not target to modify. in this case, "after mopping the floor" is the dangling modifier since it has no word to modify. the noun "house" cannot mop the floor; therefore there is a mistake in the writing of the sentence.