MathNet 2002 — Part 01 Question 88

It is given that complex numbers $z_1$ and $z_2$ satisfy $|z_1| = 2$ and $|z_2| = 3$. If the included angle of their corresponding vectors is $60^\circ$, then $\left|\frac{z_1 + z_2}{z_1 - z_2}\right| = \underline{\hspace{2cm}}$.