I couldn't put it as an answer before, but now I can. So here is my answer to your problem:
The answer has to be A because she plans to drive the distance between Buffalo and Plattsburgh (390 miles) 8 times (there and back 4 times). So just multiply (390)(8) to get 3120 miles. And the only answer choice with this number is A, so that has to be the answer.
And, just sayin', but the 300 + 90 part is just something to make you confused. It's completely unnecessary. If it's confusing you, just write the answer choices down on a separate piece of paper, putting 390 instead of 300 + 90 to make it easier to understand.