How do you find the sum of the infinite geometric series 9+6+4+...?

The sum apparently is a G.P with multiplying factor $r = \frac{2}{3}$
The equation to find the sum of an infinite G.P series with $r < 1$ is ${S}_{\infty} = \frac{a}{1 - r}$
$a = 9$ $r = \frac{2}{3}$
$\therefore {S}_{\infty} = \frac{9}{1 - \frac{2}{3}} = \frac{9}{\frac{1}{3}} = 9 \cdot 3 = 27$