1) Please have the kindness to answer this letter quickly.

请尽快赐复为感。
2) Please oblige me with a reply as soon as possible.

请尽早赐复为盼。
4) Let me know as soon as possible.

请尽早赐告。
5) RASAP Reply As Soon As Possible

请尽快答复〖网语〗
6) Please favour me with an answer.

烦请赐复。
补充资料:烦请
敬辞,表示请求:~光临。
说明:补充资料仅用于学习参考,请勿用于其它任何用途。
参考词条