Rewrite the sentences in passive voice.

1)the sister often takes bob for his brother
2)i don't know how we can solve this problem
3)unfortunately i can't find the tickets
4)they don't advise us to go there so often

1Bob is often taken for(а может ты неправильно написала ,надо-to-)his brother by the sister.
2I don't know how this problem can be solved.
3Unfortunately the tickets can't be found by me.
4To go there so often isn't advised us by them.