"这不是一个简单的问题。"

Translation: This is not a simple question.

[YoungjinSeoul]

I think 问题 doesn't necessarily mean literally a question. 'troubles' or 'problems' should be accepted as a correct answer.

[Celticfiddleguy]

一个 makes this singular in English, so problem (no 's') should be accepted. And "a simple trouble" is just not a phase that's used in English.

[davidgriff623089]

Easy and simple should both be accepted

[theLordSatan]

No, but it is a simple statement.

[Firippu_FeiLi]

Is it necessary to use 一个 in this sentence?

[R7fi9dwS]

簡単 also means easy, I think.