There are 15 chocolate bars and 10 children. In how many ways can the chocolate bars be distributed to the children, in each of the following

There are 15 chocolate bars and 10 children. In how many ways can the chocolate bars be distributed to the children, in each of the following scenarios?

a) The chocolate bars are interchangeable.

b) The chocolate bars are interchangeable and each child must receive at least one.

c) The chocolate bars are not interchangeable.

d) The chocolate bars are not interchangeable and each child must receive at least one.