Answer:
[tex]DE=3\sqrt{2}\ units[/tex]
Step-by-step explanation:
see the attached figure to better understand the problem
In this problem we have an isosceles right triangle (because has two equal sides)
so
Applying the Pythagorean theorem
[tex]DE^2=DF^2+EF^2[/tex]
substitute the given values
[tex]DE^2=3^2+3^2[/tex]
[tex]DE^2=18\\DE=3\sqrt{2}\ units[/tex]
