I think 问题 doesn't necessarily mean literally a question. 'troubles' or 'problems' should be accepted as a correct answer.
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.
Easy and simple should both be accepted
No, but it is a simple statement.
Is it necessary to use 一个 in this sentence?
簡単 also means easy, I think.