-0.3 is rational. 3.141441444... is not rational.
Explanation:
Rational number is either terminal or repeating.
-0.3 is a terminal decimal because it stops. You can write the decimal without "..."
3.141441444... is an irrational number because it is not a terminal decimal (since it has "...") and it is not repeating since the digits on the right side of the decimal are not repeating. They are changing.
3.14141414... would be repeating since "14" is repeated endlessly. However 3.141441444 is "14" then "144" and adding an additional 4 to this pattern with every iteration.