u(n) = .4s(n) +.7s(n-1)-.1s(n-1) +v(n) where variance of v(n) = .003

I want to find the cross correlation matrix against the optimal delay of 6 i.e.
E[u(n)d*(n-6)] where u(n) =column vector [u(n),u(n-1),….u(n-8)]

I can't for the life of me understand what how to get the cross correlation vector p. Could someone explain how to obtain it? I can not even find examples online. Everything seems to abstract.