Permutations help me please

Hi i need urgent help please , i don't know where this topic belongs on this forum since it seems kinda miscellaneous. Sorry to ask so much for a 1st post.

Q1) A car registration consists of 3 letters following by a number between 000 to 999

a) how many car numbers are possible?

b) How many possible car number if the 3 letters are the same?

Q2)

If repetitions aren't allowed, how many even numbers less than 400 can be made using the digits 1,2,3,4,5,6,7?

Q3) 5 travelers arrive in a town where there are 5 hotels

a) how many different arrangements if there are no restrictions on where the travelers wish to stay?

b) Suppose 2 travelers are husband and wife and must go to the same hotel. how many different accommodation arrangements are there if the other 3 can go to any of the other hotels?

Please give me some tips for these questions, i dont have a clue on how to do these, thanks alot.