The points (-4, -2) and (8, r) are located on a line of slope 1/4, We are asked to find the value of "r" that would make suche possible.
So we recall the definition of the slope of the segment that joins two points on the plane as:
slope = (y2 - y1) / (x2 - x1)
in our case:
1/4 = ( r - -2) / (8 - -4)
1/4 = (r + 2) / (8 + 4)
1/4 = (r + 2) / 12
multiply by 12 both sides to cancel all denominators:
12 / 4 = r + 2
operate the division on the left:
3 = r + 2
subtract 2 from both sides to isolate "r":
3 - 2 = r
Then r = 1