See my answer to #2.
For your part a)
For your part b) , because we have already used 4 ones. Giving each one to start with.
Hey there was wondering if anyone could give me some help with these questions or show me a link were i could get some information to help solve them.
a) How many solutions in non-negative integers are
there to the equation:
w + x + y + z = 9 ?
b) How many solutions in positive integers?
c) Use multisets to show that there are terms in the multinomial expansion of (x1+x1+.....+xn)^k