Linear means that the y values go up in a fixed increment, k. In the first one, you see that 3+4=7, 7+4=11, and so on, so you can immediately tell that it's linear.
The second one goes 3+5=8, then 8+7=15, then 15+6=21, which aren't the same numbers.
The third increases and decreases, so it's not linear.
The fourth goes 3+6=9, then 9+18=27, which you can immediately tell is not linear.
Therefore, the only linear table would be the first one.
