0$ mm, $DE = 25.0$ mm, and $\angle E = 64^\circ$. We can use the Law of Cosines to find the length of $DF$. The Law of Cosines states that $c^2 = a^2 + b^2 - 2ab\cos(C)$, where $a$, $b$, and $c$ are the sides of the triangle and $C$ is the angle opposite side $c$.
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