It is given that the queadrilateral WXYZ is a parallelogram.
By the property of parallelogram the opposite sides are equal length so it follows:
[tex]\begin{gathered} 6a+10=8a-4 \\ 8a-6a=10+4 \\ 2a=14 \\ a=7 \end{gathered}[/tex]Hence the value of a is 7.
The length WX is given by:
[tex]WX=6a+10=6(7)+10=52[/tex]Hence a=7 units and WX=52 units.