For which function will both ordered pairs (3, 6) and (4, 8) be solutions?

y = x + 3
y = 2x
y = x + 4
y = 12 - x

So you have two x-coordinate:

x=3 and x=4.

Let's test first option:

for x= 3, we have y = (3) + 3 = 6, which matches (3, 6)

Now for x=4, we have y = (4) + 3 = 7 which doesn't match (4, 8).
Do the same for any other options.

You should get B, y = 2x.