Answer
Fill the blanks with:
$(-\infty ,12)$
union
Work Step by Step
Each interval represents a set of numbers.
Numbers belonging to either of the sets belong to the UNION of the sets.
$(-\infty,9)$ contains all numbers less than 9 and $(-\infty,12)$ contains all numbers less than 12.
There is no left border of the union, so start with "$(-\infty $ ..."
and the farther right border is 12 (excluded), so we finish with "... $,12)".$
Thus, the union of the two intervals is $(-\infty ,12)$
