A spider spins a web in the following way: It starts at sea level. It moves up one inch in the first minute. It moves down two inches in the second minute. It moves up three inches in the third minute. It moves down four inches in the fourth minute. Assuming that the pattern continues, what will the spider’s elevation be after an hour has passed?

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.