Find the sum of series 4 + 44 + 444 + 4444 +------upto n terms.

Question

$\begin{array}{1 1} \infty \\ \frac{4}{9}[\frac{10(10^n-1)}{9}-n] \\44^4-4 \\ \frac{4(4^n-1)}{3}\end{array}$