The rate is constant.
Work Step by Step
In order to determine if a rate is constant, divide the change in the dependent variable by the change in the independent variable between every two points and see if they are the same. For every increase in the number of pencils by 3, the cost increases always by .75 except for the last two data points. For the last two data points, the number of pencils increases by 5, but the cost increases by 1.25. However, because .75/3 equals 1.25/5, the rate is still the same, meaning that the rate is constant.