Acar dealership sells used cars for $7,000 and new cars for $16,000. if a total of 17 cars were sold for $191,000, how many of the cars sold were used?

Let u be the number of used cars and n the number of new cars, then u+n=17.
Sales values: 7000u+16000n=191000; so 7u+16n=191.
Since n=17-u, we can rewrite this: 7u+16(17-u)=191.
7u+272-16u=191, 9u=272-191=81 and u=9. So 9 used cars were sold (8 new).