I think what we see here is that Sxmm knows what he is doing but I think he has some difficulties with the values when expanding which is mathematically correct but it leads to complications. Trebla's idea uses the previous assumption where
![](https://latex.codecogs.com/png.latex?\bg_white 9\times{9^{k}}=9^{k+1})
and that is used in the new equation after the completion of finding what
![](https://latex.codecogs.com/png.latex?\bg_white 9^{k+1})
is.