so-and-so; such and such

1. 如果他們告訴你在某某天來，你不方便就不要答應他們。
   If they tell you to come on such and such a day, don't agree if it's not convenient.
2. 他極少問自己是否喜歡某某人，他只是按照某人是否對自己有用來估價他。
   He seldom asked himself whether he liked such and such a man: he esteemed a man according to whether he was useful to himself.
3. 咱們打個比方吧，有個某某先生來旅館登記。
   Let's suppose a Mr So-and-so registers at the hotel.
4. 在求職信的開頭一定要說明你要求某某工作，理由是 ...
   Always say at the start of an application that you're applying for such-and-such (a job) because ...