Question 192000
The following was solved using a 'solver tool'. Since the x coefficients are already 1 and -1, you can ignore that part of the solution. The rest works fine.
If you want to use that tool for other similar problems, look here
http://www.algebra.com/algebra/college/linear/solving-linear-system-by-elimination.solver

*[invoke solving_linear_system_by_elimination -1, 4, 36, 1, -1, 12]