I'm kinda stuck with the following problem.
I am given the terms in Month, a net-value, a residual value, and a monthly rate. Now my job is to calculate the interest. Usually I am giving the interest and calculate anything else using the following formula:
where $n$ is the terms in month, $R$ is the monthly rate, $L$ is the net-Value, $RW$ is the residual value after $n$ months. Finally $q = (1+i)$, where $i$ is the interest.
Any idea how to solve this for $q$, i.e. the interest?