I don't know how to reply to that question. ✬

I'm sorry I didn't reply to you sooner. ✬

Sorry I didn't reply sooner. ✬

I haven't had a reply to my letter. ✬

I would appreciate a reply as soon as possible. ✬

Please write me a reply soon. ✬

I'm looking forward to your reply. ✬

I'm sorry for the delay in my reply. ✬

Thanks for your reply. ✬

Being too nervous to reply, he stared at the floor. ✬