Question

she will have combed her hair by then. change into passiv voice
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Answer 1

her hair will have been combed by her by then.

THIS IS THE PASSIVE VOICE because.

the tense of the sentence is future perfect. the formation is,

sub+ will + have + verb 3 + object + other words.

when we change it to passive,

Subject + will + have + been + V-3 + by + agent

HERE IS YOUR ANSWER.  THANK YOU.