Diagonals of a rhombus perpendicularly bisect each other. The statement can help us find a side of the rhombus. Consider the following figure.

ABCD is the rhombus and AC and BD are the diagonals. The diagonals intersect at point O.
We know

Using Pythagoras theorem in the right angled triangle ΔDOC, we get

Dc is a side of the rhombus
We know that in a rhombus, all sides are equal.
Perimeter of ABCD = 26 x 4 = 104 cm