Ребят помогите!!!

Turn from the active into the passive. By + agent is not necessary.

a) The postman delivers the letters at 8.00
b) Someone built this hotel two years ago.
c) They use a lot of preservatives in food these days.
d) Has anyone answered your question?
e) Somebody found your keys on top of the photocopier.
f) People should not take reference books out of the library.
g) They have increased the rate of taxation to forty per cent.
h) A scientist discovered penicillin in 1928.