Geometry

Question Analysis:  
This question again uses one pair of sides with known parallelism, and asks when those sides are equal in length.  
The main focus is translating a geometric condition into an algebraic equation.

Key Concept Explanation:  
To form a parallelogram with one pair of sides, you need:  
→ Parallel (given)  
→ Equal (to be solved)

Step-by-Step Solution:  
Set the expressions equal:  6x - 1 = 3x + 5
Subtract 3x:  3x - 1 = 5
Add 1:  3x = 6
Divide:  x = 2

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