Answer: The correct option is (D) 15.6.
Step-by-step explanation: As shown in the attached figure below, W is the mid-point of the line segment VX and WX = 7.8 units.
We are to find the length of the line segment VX.
Since W is the mid-point of line segment VX, so we must have

Since WX = 7.8 units, so VW = 7.8 units.
Therefore, we get

Thus, the length of th eline segment VX is 15.6 units.
Option (D) is CORRECT.