since the figure is a rhombus, the diagonals cut each other at right-angles and bisect each other, namely cut their vertices in equal halves.
what the dickens does all that mean? well, the angles at vertex C and vertex A are all twins, and therefore, ∡BCA = x, therefore
[tex]\bf (3x-26)+(x)+(90)=180\implies 4x+64=180\implies 4x=116
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x=\cfrac{116}{4}\implies x=29[/tex]
