1) I'm sorry for such~ a late reply -> (내가) 늦게 답장해서 미안해. -> (제가) 늦게 답장드려서 죄송합니다. (in a polite way) I = "내가" or "제가" : usually omit the subject "I" in Korean speech am = "해" or "합니다." sorry = "미안" or "죄송" for = "~해서" or "~드려서" late = "늦은" : but in this sentence, using an adverb form "늦게" is more natural. reply = "답장" 2) I hope you've been well. -> (난) (네가) 잘 지내길 바라. -> (전) (당신이) 잘 지내시길 바랍니다. (In a polite way) I = "난" or "전", hope = "바라다" (that) = "~하길" : We don't omit the relative pronoun usaually. you = "네가" or "당신이" : You can omit the subject "you" in Korean speech have been = "지내다" well = "잘" 3) I've been so busy and stopped using kakao talk for a while, I also couldn't practice Korean at all -> 내가 너무 바빠서 그동안 카카오톡 사용을 못했었고, 한국어 연습도 전혀 할 수 없었어. -> 제가 너무 바빠서 그동안 카카오톡 사용을 못했었고, 한국어 연습도 전혀 할 수 없었어요. (In a polite way) have been = "~해와서" or "~했었고" for using a present perfect, but you can also use "~해서" which is a present form. so = "너무" busy = "바쁘다" stop using = "사용을 못하다" kakao talk = "카카오톡" for a while = "그동안" or "잠시동안" also = "~도" couldn't = "할 수 없었다." or "할 수 없었습니다." practice = "연습" at all = "전혀"