I've been stuck with the last two problems of this question using the fundemental counting principle.

Determine the number of distiguishable four letter arrangements that can be formed from the word Germany if:

a) Letters can be repeated=2401

b) no letters repeated and:

I) there are no further restrictions =840

II) the first letter must be M = 120

III) the "word" must cointain G=?

IV) the fist and last letters must be vowels=?

Thanks for any help