Let X and Y be random variables with mean E(x)= u(1) = 1, E(y)=u(2) = 4, and variance, var(x) = 4, var(y) = 6 , and roe, p = 1/2.

Find the mean and the variance of Z = 3x -2y.The answers are -5 and 30.6

How did they get this? I know that

var(z) = var(3x) + var(-2y) +2Cov(xy)

I am not getting the right answer out for variance, and I don't really have any idea on finding the mean. Can someone break it down to me? Thanks.