How does one solve a recurrence relation like
\begin{equation} a_n=\begin{cases} Pa_{n-1} + C , & a_{n-1}=7k, k \in \mathbb{N}, k\text{ is even}.\\ Qa_{n-1} + R , & a_{n-1} =7k, k \in \mathbb{N}, k \text{ is odd}. \end{cases} \end{equation}
I know how to solve homogenous recurrence relations and non-homogenous recurrence relations of order 2. But not when there are multiple cases in them like this. Any help?