二、(10%) There are two random variables \( X \) and \( Y \). Given \( Y \), \( X \) follows the conditional distribution \( f(x|y) = e^{-y}y^x/x! \), where \( x = 0, 1, 2, ... \). Moreover, \( Y \) follows the distribution \( f(y) = \lambda e^{-y\lambda} \), where \( y > 0 \) and \( \lambda > 0 \). What are expectation \( E(X) \) and the variance \( Var(X) \)? (Please show the details)