 It is common practice supported by decided cases to assume a hypothetical tenancy, and the rateable value is an estimated annual rent which would have been agreed between a hypothetical landlord and a hypothetical tenant, on the assumption that the property in its actual physical state was vacant and to let.The landlord’s obligation to bear “the costs of repairs and other expenses necessary to maintain the tenement in a state to command that rent” implies that ordinary disrepair is disregarded in ascertaining the rateable value.However, serious disrepair which cannot be remedied or can only be remedied at an uneconomic cost should be taken into account.