Explanation:
the slope is the rate
(y coordinate difference / x coordinate difference).
between 0 and 3
x changes bt +3 (from 0 to 3).
y changes by +2 (from -2 to 0).
the slope is +2/+3 = 2/3.
between 3 and 6
x changes by +3 (from 3 to 6).
y charges by +2 (from 0 to 2).
the slope is +2/+3 = 2/3
yes, it is constant.
because, yes, it is linear. demonstrated by the graph, which is a straight line (hence the term "linear").