You can eliminate either x or y. For this problem though, since one equation has -5x, and the other +5x, it makes sense to add both equations together and very easily eliminate x.
Adding both together gives:
- -5y = 22
- y = -4.4
This y can then be substituted into either equation, to solve for x. Using the first one:
- -5x + 3(-4.4)=15
- -5x-13.2 = 15
- -5x = 28.2
- x = -5.64
x = -5.64, y = -4.4
