OME 1989 Problem 5

Consider the set $D$ of all complex numbers of the form $a+b\sqrt{-13}$ with $a,b \in Z$ . The number $14 = 14+0\sqrt{-13}$ can be written as a product of two elements of $D$ : $14 = 2 \cdot 7$ . Find all possible ways to express $14$ as a product of two elements of $D$ .