Can someone solve this problem.....I really need the solution....I have always been bad at statistics

To create polymer molecules-linear strings of monomer units linked togehter like beads on a necklace-chemists start wit monomers in solution and intiate polymerization conditions. Monomers add to the ends of growing chains one unit at a time. Because the process is random some chaings are long, some are short. There is a distribution of molecular weights.
Suppose p is the probablility that a monomer unit is reacted and connected in the chain.
a) show that distribution of chains with length k is
p_{k}=n_{k}\sum_{k=1}^{\infty} n_{k} with n_{k}=p^{k-1}(1-p)
b) calculate the average chain length
<k>=\sum_{k=1}^{\infty}kp_{k}
in experiments one measures the molecular weight distribution w_{k}=kn_{k}/\sum_{k=1}^{\infty}kn_{k}
c) show that
w_{k}=k(1-p)n_{k}
d) compute the average molecular weight
<m>=\sum_{k=1}^{\infty}kw_{k}