Final answer:
EF = DE = ∡D is equal to 90°.
Step-by-step explanation:
The question states that EF = DE = ∡D. Since all three measures are equal, we can use any of them to find the value. Let's choose ∡D = 90° as an example. Since the measures are equal, EF and DE must also be equal. Therefore, EF = DE = 90°.