Answer: 384 square units
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Step-by-step explanation:
Let A = (4,8) and B = (12,16)
Form point C at the location (12,8). Note how points A and C are on the same horizontal level, or they have the same y coordinate.
The distance from A(4,8) to C(12,8) is 12-4 = 8 units. Ignore the y coordinates and subtract the x coordinates. This trick only works for horizontal line segments.
So we can see that each square face has a side length of 8 units. The area of each square face is 8^2 = 8*8 = 64 square units.
There are six of these faces, so 6*64 = 384 square units is the total surface area of the number cube.