Let N,X1,Y1,X2,Y2,… be independent random variables. The random variable N takes positive integer values and has mean a and variance r. The random variables Xi are independent and identically distributed with mean b and variance s, and the random variables Yi are independent and identically distributed with mean c and variance t. Let

Question

A=∑i=1NXiandB=∑i=1NYi.
Find cov(A,B). Express your answer in terms of the given means and variances using standard notation.

cov(A,B)= - unanswered
Find var(A+B). Express your answer in terms of the given means and variances using standard notation.

var(A+B)= - unanswered