Clarissa wants to create more shade in her yard to block the hot sun, so she buys a sapling of an oak tree and plants it in the yard. To make sure the tree is growing at a healthy rate, she makes the following table to track its height over a period of weeks. What is the average rate of change in the tree's height from week 3 to week 9? Enter your solution into the box below.

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.