Determine which system below will produce infinitely many solutions.
Select one:
a. −6x + 3y = 18
4x − 3y = 6

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

c. 3x − y = 14
−9x + 3y = −42
d. 5x + 2y = 13

−x + 4y = −6