Translation:Vâng, tạm biệt.
-"khoẻ" means like "in well being/good health", which is why you hear people say it while saying "i'm fine" as "toi khoẻ."
-"dạ" means "yes" in the southern dialect. but on duolingo, you'll see them use "vâng" as yes, since that is northern dialect. both are correct words for yes though.
-"có" means have or possess. you can hear it in a range of ways:
"bạn có đồ ăn không?" (do you have food?) - "có". (this literally just means have, but in this scenario it means you do have it, but in a way its like you are saying yes to the question). sometimes people would say "vâng, có" (yes, have) too as a response, but "có" itself is just a shorter way
"bạn có khỏe không?" (how are you?) - vâng, toi có khỏe (yes, im fine) it's not necessary to use có in this type of scenario but you do hear it sometimes. it's basically just saying have well-being.