Answer
$(-\infty,9)$, intersection
Work Step by Step
Step 1. The interval $(-\infty,9)$ represents the values to the left of point $x=9$ on a number line.
Step 2. The interval $(-\infty,12)$ represents the values to the left of point $x=12$ on a number line.
Step 3. The elements common to both of above is then $(-\infty,9)$ which represents the intersection of the above intervals.
