question

A person died on the 31 july 2022. her husband died on 30 june 2019 and left his estate to her. he used 20% of his 325000 nil band on lifetime gifts. her estate consists of a residential property valued at 450000 which she has left to her children and she has made no lifetime gifts.
how much nil rate band is available on her death.
Why is the answer not 585000. why is the answer 935000 whilst there is no mention of a main residence. it is mentioned in the notes that residence nil rate band should only be assumed when there is mention of a main residence.
the question is from acca december mock exam