Question

Question about Permutations/Combinations

Hi, here are the questions... I'm really having difficulty thinking this through... can anybody help?

How many different 4-letter ‘words’ (i.e. arrangements of 4 letters) can be formed using
only letters appearing in the given word, if each letter can be used (only) as many times
as it appears in the given word? (State your final answer to each as a single number.)
(a) parsec
(b) papers
(c) rapper
(d) pepper