Diana wanted to make peanut brittle for a holiday party, so she bought a 16.5-ounce jar of peanuts at the grocery store. She used of the peanuts to make peanut brittle. The next
week, she split the remaining peanuts into 3 bags of trail mix for a hike with friends. How
many ounces of peanuts did Diana put in each bag of trail mix?

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.