First, see if you can eliminate answers by Ballparking, which can also work on algebra questions. To go from 16x to 8x, you would just divide by 2 . Dividing 30 by 2 gives you 15 , so 28 is way too big. Eliminate it. The correct answer is not likely to be 15 , either, because that ignores the −2 and the −4 in the question.To solve this one, add 2 to each side of the equation to get 16x=32. Divide both sides by 2, which gives you 8x=16. But don't stop there! The full question asks for 8x−4, so (C) is a trap answer. You have to take the last step and subtract 4 from both sides to find that 8x−4=12, which is (A).