The answer is 16m.
To find this, note we are only looking at the time between t=6 and t=10. In this time, the object moves from x=8 to x=16 until it turns around and moves back to x=8.
Looking at the distance, we see that we just add the absolute values of the change in x, getting abs(16-8) + abs(8-16) where abs means absolute value.
This gets the answer 8+8 which is 16.