3x < 12 what is this in the interval notation

Divide by 3 to find the solution.

x < 4

Interval notation uses parentheses around the lower and upper limit of the interval. Here, the lower limit is - ∞ and the upper limit is 4. The parentheses are round () if the limits are NOT included as part of the interval. They are square brackets [ ] if the limits are included in the interval.

Here, since - ∞ is not an actual number, we use the round bracket on that end of the interval. Since the solution space does not include 4, we use the round bracket on that end of the interval as well.

The solution to your inequality is ...

(-∞, 4)