Solve the following problem:
Assume that random processes X(t) and Y (t) are individually and jointly stationary.
a. Determine the autocorrelation function of Z(t) = X(t) + Y (t).
b. Determine the autocorrelation function of Z(t) when X(t) and Y(t) are uncorrelated.
c. Determine the autocorrelation function of Z(t) when X(t) and Y (t) are uncorrelated and have zero means.