Answer: $8
From the table given, we obtained the below information
Number of cars Money ($)
5 40
10 80
15 120
20 160
Calculate the constant rate of change in dollars per car
For the first given data
The total number of cars washed is 5
The total money to washed the 5 cars is $40
Rate of change in dollars per car = Total amount of money / the total number of cars
Rate of change = 40 / 5
= $8
The same procedure applicable to the rest data
For 10 cars and $80
The rate of change in dollars per car =80/10
= $8
For 15 cars and $120
The rate of change in dollars = 120 / 15
= $8
For 20 cars and $160
The rate of change in dollars per car = 160 / 20
= $8
The constant rate of change in dollars per car is $8
The answer is $8