The diagonals of a rectangle have equal lengths. Since AC has a length of 28, and AC is a diagonal, the other diagonal BD also has a length of 28. The diagonals of a rectangle also bisect each other. So diagonal BD is bisected by the other diagonal AC at point E. And since diagonal BD has a length of 28 then BE and ED both have a length which is of 28, or 14 each.
Answer: ED has a length of 14.