Let A = [1, 2] and B = [3, 4].

We have:

A = {1, 2} and B = {3, 4}

Now,

$n(A \times B)=n(A) \times n(B)=2 \times 2=4$

There are 2n relations from A to B, where n is the number of elements in their Cartesian product.

∴ Number of relations from A to B is 24 = 16.