Question 2
Let $O_1$ and $O_2$ be two disjoint circles with integer radii $R$ and $r$, in cm, respectively, where $R\gt r$. The distance $d$, in cm, between their centres is also an integer. The length of each external common tangent segment is $\sqrt{504}$ cm, and the length of each internal common tangent segment is $\sqrt{408}$ cm. What is the value of $d$?
