The rule for reflecting over the y-axis is simple. Say you have the points (-8, 7) and you plot them on the graph. Your question says to reflect those points across the y-axis. Your new coordinates would then be shown as (8, 7). As you can see, the x-value is now the opposite of the x-value before reflecting across the y-axis. I hope this helped.
Since the slope of the line is (31/4 - 25/4) / (5/4 - 3/4) = 3 that means that for every 1 that x increases, y increases by 3 so an example could be 1 3/4 for x and 9 1/4 for y.
