Ok, we start knowing
Eq.1) 9x - 3y = 12
Eq.2) 3x - 5y = 7
Solve 6x - 2y = ?
Are you sure you wrote that last line out correctly? Are you sure it's not
6x + 2y = ?
Because you can subtract Eq2 from Eq1 or
9x - 3y = 12
[ 3x - 5y = 7]
to get
6x + 2y = 5.
It's so neat, and so nearly the answer... And the alternative is to solve for x + y, which gets time consuming and opportunity for error.
In fact, I've had several goes now at solving x and y, and the numbers don't check out when plugged back in, which makes me think even more that there is a mislaid - or + sign somewhere in this group of equations.
