Answer:
It depends on the positions of the points.
Explanation:
Since there is no figure, we cannot tell what the correct answer is since there is more than one possibility.
Here is one valid possibility.
10 5
<----------------+--------------------------+------------+--------------------->
A C B
Here we have point C between points A and B. Then according to the definition of a point between two points, we have AB = AC + CB.
AB = AC + CB
AB = 10 + 5
AB = 15
Here is another equally valid possibility.
<----------- AC = 10----------------->
5
<----------------+--------------------------+------------+--------------------->
A B C
Here we have AC = 10 and CB = 5, but we have point B between points A and C. According to the definition of a point in between two points, we have AC = AB + CB
10 = AB + 5
AB = 5
AB may be 10 or 5 depending on the order of the points on the number line. That makes the problem ambiguous without a figure.