Take any two points -- I'm using (0, 1) and (1, 3). You can think of slope as (change in y)/(change in x), or simply rise/run. (3-1)/(1-0) is equal to 2.
*Note: (-1/2,1/2) is not in the same line as the other four points.
The student is incorrect because if they were to reflect point A over the X-axis, this would mean they are moving it from its current quadrant to the one below. In that quadrant, the Y coordinate will be negative. So it couldn't possibly (6,3), because the 3 isn't negative.
