Explanation:
the slope of the line is expressed as the ratio
y coordinate change / x coordinate change
when going from one point to the other.
we have 2 points marked on the chart :
(6, -1) and (9, 3)
x changes by +3 (from 6 to 9)
y changes by +4 (from -1 to 3)
the slope is therefore +4/+3 = 4/3