That’s just 0.6 and 0.0 written cleverly.
If the 9’s repeat forever then there is no possible number between that and 0.6, so it must be the same…
Put another way, any single digit “n” repeating is just n/9.
Your problem is equivalent to (4/9 + 5/9 - 0.4) + 0/9
(Equivalent to 0.6)