In a triangle $PQR$, $PS$ is the angle bisector of $\angle QPR$ and $\angle QPS$ = $60$°. What is the length of $PS$ ?
1. $\frac{(q+r)}{qr}$
2. $\frac{qr}{(q+r)}$
3. $\sqrt{(q^{2}+r^{2})}$
4. $\frac{(q+r)^{2}}{qr}$