To find the length of segment $AB$, we use the formula for the distance between two points on a number line, which is the absolute difference between their coordinates:

$AB = |B - A|$

Here, the coordinates are $A = -31$ and $B = -13$.

So, the length $AB$ is calculated as:

$AB = |-13 - (-31)|$

Simplifying the expression:

$AB = |-13 + 31| = |18| = 18$

Thus, the length of $AB$ is $\boxed{18}$.

Would you like further details or have any questions?

Related Questions:

1. How do you find the distance between two points in the coordinate plane?
2. What is the midpoint of a line segment given its endpoints?
3. How can we apply this distance formula to three-dimensional space?
4. Can you explain the concept of absolute value and its importance in this calculation?
5. What are some real-world applications of finding the distance between two points?

Tip:

When dealing with distances on a number line or a coordinate plane, always remember that distance is a non-negative value, hence the use of absolute value.