Okay so when you need to find an equation that is infenetely many solutions, both equations needs to be equal like x=x so when x is 2, it is 2=2 whatever number you put, they are equal. That's why it is infenetely many solutions.
First, lets simplify the equation
3y=9-6x (the common number is 3 so lets divide them all to 3 so we will have one variable on one side all alone which is y)
y=3-2x
Let's look at the answers. We need to leave y on one side.
A. y=3-2x
B. y=9-2x
C. y=2x+3
D. y=-2x+9
When we simplify the equation on the top, we got y=3-2x so the answer is A
Hope it helped :)