ANSWER:
30 cars
STEP-BY-STEP EXPLANATION:
The first thing is to calculate the total cost for 4 people, like this:
[tex]100+360+50\cdot4=660[/tex]Now, we must subtract the budgeted value, to know the amount they need to complete the total cost of the trip, like this:
[tex]660-485=175[/tex]The four students decided to earn the additional amount by washing cars.
They charge $6 for each car wash. Therefore, the number of cars to get $175 would be:
[tex]\begin{gathered} c=\frac{175}{6}=29.17 \\ c\approx30\text{ cars} \end{gathered}[/tex]Because if they wash 29 cars, they will not be able to reach the necessary amount, they must wash at least 30 cars