So we are given two points of the line:
p1(2, 8), p2(6, 12)
with them we can calculate the slope of the line like this:
m = (y2 - y1)/(x2 - x1)
where x1,x2, y1,y2 are the coordinates of the points p1 and p2
m = (12 - 8)/(6 - 2) = 4/4
m = 1
therefore the line slope is 1