Answer: AB = 14 units.
Step-by-step explanation:
Collinear means that we can draw a line that goes trough the 3 points.
We also know that B is between A and C, so we may have something like:
----A---------B--------------C------------
The distance between A and C is 18 units.
And the distance between B and C is 4 units.
Looking at that description, you can see that the distance between A and B is equal to the distance between A and C minus the distance between B and C.
So we have:
AB = AC - BC = 18 units - 4 units = 14 units.
