一両日中にはっきりしたお返事を差し上げます - lucifuge @Wiki

「一両日中」は暗誦用例文の

There are so many places in London. I'm afraid you'll not be able to see all of them in a day or two.

の後半部分を拝借する。

I'll give you a definite reply in a day or two.

回答例

You shall have a definite answer in a day or two.