For the case of the Number greater than 3000
Let us make the choice form where :-
1st Position has 2 choices to make from (3 or 4)
2nd Position has 3 choices to make form (2 or 3 or 4)
3rd Position has 3 choices to make form (2 or 3 or 4)
4th Position has 3 choices to make form (2 or 3 or 4)
Hence total of 2*3*3*3 = 54 Choices
But here we have done a mistake as it can include number such as 4222, 3222 and 3333. So we need to subtract these.
Hence net resultant will be = 54-3 = 51 Choices.