In the year 2017, n = 1 and D(1) = 4.5 + 0.11(1) = 4.61
In the year 2018, n = 2 and D(2) = 4.5 + 0.11(2) = 4.72
In the year 2019, n = 3 and D(3) = 4.5 + 0.11(3) = 4.83
The slope of D(n) = 4.5 + 0.11n is 0.11 and it determines the gradual increase in the average consumer debt every year.