Dollars is the dependent quantity because the amount you pay depends on how many gallons you've pumped.
Answer:
Nifal received $ 4 for washing the first car.
Nifal received $ 5 for washing the second car.
4 and 5 have a sum of 9.
Step-by-step explanation:
The problem can be rewritten as follows: Find the sum of two consecutive entire numbers equal to 9. That is:


Then, by eliminating y:

Now, let is clear
:


Nifal received $ 4 for washing the first car.
The earning for the second car is: (
)



Nifal received $ 5 for washing the second car.
4 and 5 have a sum of 9.
They mowed total of 11/15 (5/15 + 2/5) already, so they still have 4/15.