To find the slope of a line given two points, you should use the formula, Slope=y2-y1/x2-x1.
In this exercise is given a graph showing the coordinates of two points and it is asked to find the slope of the line which intercepts both points, which coordinates are (0,6) and (3,0). To find the slope, you should substitute the given coordinates into the previous mention formula.
Slope=y2-y1/x2-x1
Slope=(6-0)/(0-3)
Slope=6/-3
Slope=-2
The slope of the lines which passes through the coordinates
(0,6) and (3,0) is -2.