My proof goes like this: Let $x=0.134888⋯$
$1000x=134.888⋯$
$1000x=134+0.888⋯$
$10000x=10(134+0.888⋯)$
$10000x=1340+8.888⋯)$
$10000x−1000x=1340+8.888⋯−(134+0.888⋯)$
$9000x=1340−134+8.888⋯−0.888⋯$
$9000x=1214$
$$x=\dfrac{1214}{9000}=\dfrac{607}{4500}$$
Then I concluded that this is a rational number. Any feedback is greatly appreciated. Thank you,
Note that ${1 \over 9} = 0.\bar{1}$, so $0.\bar{8} = {8 \over 9}$.
Then $0.134\bar{8} = {134 \over 1000} + {1 \over 1000} {8 \over 9}$.