In order for the parallelogram to be a
rhombus, x = [?].
(5x + 25)
(12x + 11)

A parallelogram is also a rhombus if the diagonal is a bisector of an angle enclosed by the two adjacent sides of a parallelogram.
In our case it means,
[tex]5x+25=12x+11[/tex]
[tex]7x=14\implies x=\boxed{2}[/tex]
Hope this helps.