So EB 1 is parallel to AB.
Therefore, the distance from point E to the plane is converted into the distance from B 1 to the plane.
Let the midpoint of BC 1 be OB 1 and the vertical BC 1.
So, B 1O is what you want.
B 1O is the root of 2.
So the distance from e to the plane ABC 1D 1 is the root of 2/2.