Solve each system of equations.
1. 3x + y = 7; 5x +3y = -25
2. 2x + y = 5; 3x - 3y = 3
3. 2x + 3y = -3; x + 2y = 2
4. 2x - y = 7; 6x - 3y = 14
5. 4x - y = 6; 2x -y/2 = 4