Problem 198: A class used cars and buses for a field trip. They used 6 vehicles for this trip. Each cars hold 5 students and each bus holds 30 students. If 80 students went to the trip how many of each vehicle did they use?
Solution: Let 
be the amount of cars used and 
the amount of buses used. That is, we have 
so that 
. Hence,
(1) 
Now that we know we can find . Thus
(2) 
Therefore, they used 4 cars and 2 buses for the trip.
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