there are a few ways to go about this. In this case I think the easiest is to just list the roll sequences that make up $A \cap B$ and find their probabilities.

$A \cap B$ is pretty clearly $(1,4), (1,5), (1,6), (6,1), (6,2), (6,3)$

Each event of rolling 2 dice has a probability of $\left(\dfrac 1 6\right)^2=\dfrac 1 {36}$

There are 6 events in $A \cap B$ so the total probability is $6 \times \dfrac 1 {36} = \dfrac 1 6$