So we are given two points of the line:
p1(4,9), p2(2,9)
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 = (9 - 9)/(2 - 4) = 0/-2
m = 0
therefore the line slope is 0,
you can also see it because is parallel to the x axis, therefore its slope is zero
