GRE Sample Test 2 Quantitative Reasoning 2

To find the area of a square, you need the length of a side. To find a side, find the distance between two vertices. If A is at (3, 7) and B is at (3, 12), then the length of a side is equivalent to the difference in the y- coordinates: 12 − 7 = 5. So, side AB has a length of 5.
Square this to find the area: 52 = 25. The fact that there are variables for the y- value of points C and D is irrelevant to solving this problem.