Yes, you're more likely to see 弁当. Both of these kanji are learned in elementary school, so even kids can read them.
Do you mean simplified in relation to traditional Chinese hanzi? Japanese kanji were simplified at some point, but are different from Chinese simplified characters.
This question leaves me a bit confused, shouldnt they be asking for the translation of "lunch"instead of "bento" and then the answer would be べんとう, i feel this would be a more pertinent question to translate both the meaning and the phonetics but maybe theres something im not getting ? or maybe its just meant to be this way?
If you read the other comments you should be able to find your answer, but I think the main source of confusion is that "bento" is an English word (a loan word from Japanese). The English translation of べんとう is bento (or boxed lunch or lunch box, depending on the context). If you're transliterating べんとう into romaji, it's bentou or bentō, not bento.