The unit rate is the rate of change per day or the slope.
To get the slope of the line, we use the slope formula:

Where
is point 1 on the line and tex](x_{2},y_{2})[/tex] is point 2 on the line.
Let's take 2 points from the line and calculate the slope. We will take the points (0,0) and (1,3) (any two points on the line will give the correct answer).

This means Barton reads 3 chapters per day. Answer choice C is right.
ANSWER: C