Use generating functions to find $a_{n}$ if:
$a_{n} =6n+a_{n−1}$, for $n≥1$ and $a_{0} =0$
I tried to divide it into two separate sums $\sum_{m=1}^\infty 6mx^m $ and $\sum_{l=1}^\infty a_{l-1}x^l $
I have managed with the left sided sum, but then I realized that on the right side I do have sequence in a sum and now I am a bit confused and I don't have idea what to do now.