Which system of equations has infinitely many solutions?

A) 6x + 3y = 12

3x + y = 9

B) 2x + 3y = 6

4x + y = 8

C) 12x + 9y = 6

4x + 3y = 6

D) 5x + 10y = 20

2x+4y=8

D)

If you multiply 5x+10y=20 by 2 and 2x+4y=8 by 5 that are equal

The answer is D.

Divide the first equation by 5 to get

x + 2y = 4

Divide the second equation by 2 to also get

x + 2y = 4

Since they are the same equation it results in an answer that has infinitely many solutions.