Unable to answer "What is the house number of this building?" for https://osm.org/way/153506930 via StreetComplete 31.0:

It appears to be either a rental unit or a detached "den" / living room. but it could also be a very nice shed. either way, it does not have a separate address from the main house, #89. Not sure if it should be tagged as no address or #89.