Whats the diameter and radius? (I'll solve the rest this is just confusing...)

Answer:
425
Step-by-step explanation:
By right angle triangle with sides 20 5
we can find hypotenuse
hyp^2 = 20^2 + 5^2
= 400 + 25
= sqrt(425)
then for all sides it is same length
Area of shaded region = side^2
= 425