This means that the area of the ellipse is 2 times the area of the circle.
Thus the red section is twice that of the blue section.
Do you understand how to get the above formula? It's just the area of the circle, minus the area of the square, all divided by 4.
The area of the square is easy, because you're given the length.
The area of the circle is NOT so easy, because you're not given the radius. But you can find it.
Notice that the diagonal on the square is actually the diameter of the circle?
So you can find the diameter using Pythagoras, and then halve it.
Hope that helped