色々な言い方がありますが質問に近い回答を選びました。
That is a tough question to answer.
それは[回答](https://eikaiwa.dmm.com/uknow/questions/44064/)するには[難しい](https://eikaiwa.dmm.com/uknow/questions/36244/)問題です。
それかはっきりと
I have no comment on that.
私はそれに対してコメントはありません。
と言ってもよいかもしれません。
I really don't know what to say. That's something you need to think about.
Might be "easier said than done."
1) The phrase "let me get back to you" shows that you will think about the situation and get back to them when you have an opinion, advice or maybe even a solution.
2) Lets them know that the situation they are in isn't something you can solve but is something they need to deal with. Letting them know that they "need to think about it" shows that it's a serious problem.
3) "Easier said than done" means that the situation they're in is most likely more difficult than it really seems.
1) "let me get back to you"というフレーズは状況を考慮し、意見やアドバイス、解決法が思いついたら返事をします、という意味です。
2)解決できない問題に直面している状況であるが、避けて通れないことを知らせています。相手に"need to think about it"（考えなければならない）と知らせることは、問題を重く捉えているいることを意味しています。
3) "Easier said than done"は、陥っている状況が見かけよりも難しいようだという意味です。
examples
"well, you stumped me with that question,
that's a hard one to answer".
or
"that's a tough nut to crack".
or
"that's a difficult question to answer".
or
"that's a tough one!".
例
"Well, you stumped me with that question,
that's a hard one to answer".
（それは難しい質問ですね。答えるのは簡単ではありません。）
または
"That's a tough nut to crack".
（それは難しい質問です。）
"That's a difficult question to answer".
（それは難しい質問です。）
"That's a tough one!".
（それは難しい質問です。）
▪ What a difficult question.
This is saying directly that the question is hard to answer.
▪ You caught me off guard with that question.
off guard is to be unprepared.
This is saying the he/she has surprised you with the questions which makes it difficult to answer.
▪ What a difficult question.（なんて難しい問題でしょう）
これは直接的に答えることが難しい問題だということを言っています。
▪ You caught me off guard with that question.
（その質問には答える準備ができていないです。）
"off guard"は準備ができていないことです。
答えることが難しい問題でびっくりしている事を言っています。
Tough', in the context of a question, means that is hard and difficult to figure out. The 'one' refers to the question itself.
A 'head scratcher' is a question that makes you think hard to find the answer. When a person thinks about something a lot, they may scratch and rub their head to help them think and concentrate, and that is where this popular phrase comes from!
That is a "difficult one" to answer= Without having to use the word question you can let the person know that their question was a little tough to answer. The word "one" then becomes the subject of the sentence.
That is "not an easy" question to answer= Easy is the opposite of difficult. Easy is a generally viewed as a positive word.
"Not an easy" this is a polite way of expressing how difficult you feel the question is.
Not- is used for negation
Negation: a negative thing or condition
Example of negation: I *do not* feel happy about this.
Rather than: I feel sad about this.
That is a "difficult one" to answer= questionという単語を使わなくても、相手に彼らの質問は少し答えるのが難しいと伝えることができます。"one"という単語は質問文を指します。
That is "not an easy" question to answer= easyはdifficultの反対語です。easyは一般的にポジティブな単語です。
"Not an easy"はその質問がどれだけ難しいのか丁寧に表現する言い方です。
Notはnegation（否定する）に使われます。
Negation:ネガティヴなことや状況
Negationの例:
I feel sad about this.（これについて悲しいです）
と言うより、むしろ
I *do not* feel happy about this.（これについて幸せではない）
Wow, I have to get back to you on that one. That is a tough question.
That is tough question to answer.
The answer is so difficult, I'm not sure I can answer this question.
Tough and difficult questions most time come with tough and difficult answers. And it can be a lot for people to be asked those type of questions. You can excuse yourself and say that you are up for that type of discussion.
アメリカ合衆国 
日本 
イギリス 
南アフリカ 
