If the system of equations
3x + y = a
2x + 5y = 2a
has a solution (x,y) when x = -2, compute a
First, substitute -2 into x.
So...
-6+y=a
-4+5y=2a
If we double the first equation, then -12+2y=2a. Subtract the first and second equations, and you can solve the rest from there
