Which system of equations has exactly one solution?
1. 3x - y = 4
9x - 3x = 12
2. 2x - y = 3
2x - y = -4
3. 8x - 3y = -12
x - 3y = 9
4. 5x - y = -3
5x - y = -2
The system of equations that has exactly one solution is:
4. 5x - y = -3
5x - y = -2