Poisson distribution

[barabbas]

Hi, would be thankful if someone could help me out here.

Let N be P(λ)-distributed and X|N = n be Bin(n,p)-distributed. Find E(X) and V(X).

First I take

p x,n (y) = bin(pdf) * Po(pdf)
p x (y) = sum bin(pdf) * Po(pdf)

How do I continue from here?