Questions that ask that (simplify the result) might as well also ask how long a piece of string is ....

The fact is that different people will have a different idea of what simplify the result means ....

However, since the basic answer can pretty much be written down by inspection in one line, I suspect the writer of the question wants you to factorise the answer. In which case, s/he should have just said to give your answer in factorised form.

Personally I find the use of broad instructions such as "simplify your answer" and their ilk ridiculous in many cases. In your case, I would have thought that the intent of the question was to test a basic skill (use of product rule), that the question would be worth 1 mark and that your answer would be sufficient. In which case, the instruction to "simplify the result" is even more ridiculous since potentially a student could get zero even though s/he has succesfully applied the skill.

Such instructions are especially potentially ridiculous in on-line tests. In my opinion, such a broad instruction usually makes the person who wrote the question look like a fool.

Instructions I typically use include:

".... and completely factorise your answer."

"Express your answer in exact surd form."

"Find in exact form ...."

"Find in the form where a, b and c are whole numbers ...."

"Find in the form y = mx + c the equation of the line ...."

etc.

In other words, I specifically prescibe the form I want the answer in.