Answer:
Difference = 2
Explanation:
Coordinates of location of Annie = (3, 5)
Initial(But Wrong) Coordinates of location of Barbara = (-6, 2)
They agreed to meet at the midpoint of their current location. The formula to calculate the midpoint is:

Using the values in the above formula, we get:

Correct Coordinates of location of Barbara = (-10,4)
So, the correct midpoint between location of Barbara and Annie would be:

The x-coordinate of initial mid-point = -1.5
The x-coordinate of actual mid-point = -3.5
The positive difference between the x-coordinates = | -3.5 - (-1.5) |
= | -3.5 + 1.5 |
= | -2 |
= 2
The positive difference in the x-coordinates of where they agreed to meet and where they should actually meet is 2