To solve for $x$ in the given diagram, let's analyze the geometry provided:

1. Identify the Shapes and Their Properties:

   • The figure consists of a rectangle $ABCD$ with side lengths $AB = CD = x$ and $AD = BC = 4$ cm.
   • There is an additional triangle $EFD$ outside the rectangle.
   • Points $E$ and $F$ are connected to vertices $A$ and $D$, forming triangle $EFD$.
   • Given that $\angle EDF = 90^\circ$, it suggests right triangle properties.

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