Answers by MR. ROBOT

The sum of $n$ terms of the series $4+44+444+\ldots .$ is $(4 / 81)\left[10^{n+1}-9 n-1\right]$$(4 / 81)\left[10^{n-1}-9 n-1\right]$$(4 / 81)\left[10^{n+1}-9 n-10\right]$...