3. Determine all values of $k \in \mathbb{R}$ for which the equation
$$
\frac{4\left(2015^{x}\right)-2015^{-x}}{2015^{x}-3\left(2015^{-x}\right)}=k
$$
admits a real solution.
3. $k \in\left(-\infty, \frac{1}{3}\right) \cup(4,+\infty)$