You must evaluate each of statements (1) and (2) completely independently. If neither work, then you would go ahead and consider the two statements combined. If even that doesn't give you a solid answer, then you would choose (E): Not enough information to answer the question.

This is the math section the GMAT is most famous for. It makes you think in a way that isn't so straight forward and so requires a little getting used to. Take this opportunity to familiarize yourself with this question format type. Remember, the goal is not to calculate everything - it's to figure out of the data provided is sufficient to answer the original question.

All questions in data sufficiency have the exact same list of answer choices. So it is in your best interest, to memorize what each answer choice corresponds to. 

(A) is when Statement (1) alone provides enough information to definitively answer the original question--but not statement (2). 

(B) is when Statement (2) alone provides enough information to definitively answer the original question--but not statement (1).

(C) is when (1) and (2) by themselves are no good - but when combined, you do have enough information to answer the question.

(D) is when either (1) or (2) by themselves work

(E) is when neither (1) nor (2) provide enough information - effectively saying the data provided is not sufficient to answer the question.