Translation:Please do your homework quickly.
I wrote 'please quickly do your homework' as well and was marked incorrect.....
I can't say why, but your answer sounds really wierd to me. I speak American english.
As an expression (i. e., not a literal translation), couldn't this also mean "Hurry up and do your homework")...?
I wrote "please hurry up and do your homework" and it marked it incorrect and said the correct phrase was "please hurry up and finish your homework"
As someone raised in a Japanese household, that is how I internalize it.
I think yaru is more casual. I've only come across it personally in casual speech, but not 100% sure.
Ignore that. I looked it up. Yaru is okay for physical actions (and also can mean give, but usually implies a level of looking down) whereas suru can be used for physical or mental actions. Duo really needs a tips and notes for this, rather than achievements and clubs and whatnot. We can do without those! Priorities, yo.
I think you use yaru when giving to animals something or to your younger brother.
I really think I have read that in a textbook.
You can, because "fast' is a "flat/bare adverb" (that is, an adverb that doesn't end in "-ly"). Moreover, the adverb "fast" doesn't even have a competing "-ly" form, so prohibiting its use isn't even an option. However, the traditional view (which came from 18th century grammarians) was that all adverbs should end in "-ly". Quoting Wikipedia, "despite bare adverbs being grammatically correct and widely used by respected authors, it can be advisable to instead use the forms with -ly because these are often considered more socially accepted and of higher status". Very interesting references about this topic are this Grammar Girl's article and this Merriam-Webster's video.
Could I use "quickly" right before the verb? Like this:
Is this correct too?
"Please hurry and do your homework" didn't work, and was replaced with "Please hurry UP and do your homework."
Early isn't really implied except in a loose, sooner than later sense. That's actually what is meant by "quickly". If you really want to mean early, that would be would be 早めに. You could also add a modifier like 出来るだけ早くor なるべく早く.