Solve each linear system by elimination or substitution: x+y=-8 and 3x-y=12

To solve the system by elimination, we can add the two equations together to eliminate y:

x + y + 3x - y = -8 + 12
4x = 4
x = 1

Now, we can substitute x = 1 back into one of the original equations to solve for y:

1 + y = -8
y = -9

Therefore, the solution to the system of equations is x = 1 and y = -9.