Translation:Big brother, take care.
Bad test question. This is not translatable into English. It is a Japanese custom that does not have an equivalent in English culture. In Japan, when someone leaves the house, he says "行ってきます！” Those who are not leaving the house, say, "いってらっしゃい！” But you don't say it when you leave work or anywhere other than your home. The 2 phrases mean the same thing -- go then come back! English speakers often don't say anything when they leave. It does not mean "have fun" or "see you later." You're just acknowledging that someone is leaving and you expect them to come back later. The closest translation in English is "y'all come back now, hear?" But that's for an extended outing, not for every day. The Japanese custom is for everyday leaving and returning.
So should this question be removed because there's no English equivalent? I do appreciate the more detailed explanation, but I think "literal" translations that don't have the same cultural meaning are okay because they are necessary for an understanding of the language. Or are you suggesting that the translation for 行ってきます and いってらっしゃい be changed to / added as "I'm leaving and coming back" and "Go and please come back"?
Perhaps they could put the closest English alternative they can (have fun, come back soon, whatever) but include an asterisk you could click on to read a deeper explanation. Maybe that is beyond the scope of duolinguo... In any case, I sure am grateful for these threads! Thanks to all who contribute much needed info