Determine which system below will produce infinitely many solutions.

1. −6x + 3y = 18
4x − 3y = 6

2. 2x + 4y = 24
6x + 12y = 36

3. 3x − y = 14
−9x + 3y = −42

4. 5x + 2y = 13
−x + 4y = −6