1. A company buys a digital scanner for $12,000. The value of the scanner is 12,000 (1 – 3) after n years. The company has budgeted to replace the scanner when the trade-in value is $2,400. After how many years should the
company plan to replace the machine in order to receive this trade-in value?

Sorry not sure. :

So the first thing we do is to multiply the top equation by 3. the reason i want to do this is i notice there will be a 6y on both equations and can possibly add/subtract them. so we get 6y = -3x + 27. adding that and the second equation we get 6x = 27-15 which is 12. divide by 6 and we get 2. ∴ x = 2. substituting 2 into the first equation we get 2y = -2 + 9 which is 7. divide by 2 and we get 7/2. ∴ y = 7/2, x = 2.