Geometry

Question Analysis:  
This question involves using one pair of opposite sides that are already parallel, and finding when they are equal, too.  
The main focus is on applying the condition: If one pair of opposite sides are both parallel and equal in length, then the quadrilateral is a parallelogram.

Key Concept Explanation:  
To prove a quadrilateral is a parallelogram, it’s enough to show:
- One pair of opposite sides is parallel (already given)
- That same pair is equal in length (to be solved)

Step-by-Step Solution:  
Set the expressions for AB and CD equal:  2x + 5 = 5x - 4
Subtract 2x:  5 = 3x - 4
Add 4:  9 = 3x
Divide by 3:  x =...