Calculate the value of a series using z-transform

Question

I want to calculate the value of the following series

$\sum_{n=1}^\infty\big(\frac{2}{5}\big)^n$

For this I use the z-transform which gives:

$X(z)=\sum_{n=1}^\infty\big(\frac{2}{5}\big)^nz^{-n}$

From the table of z-transforms, we have $a^n=\frac{z}{z-a}$, thus, with $a=\frac{2}{5}$:

$z-transform: a^n =\frac{z}{z-\frac{2}{5}}$

but from here, I am not sure what to do.

Thanks