I want to find the expected value and variance of these models but I am not quite sure what I need to do. The error term (white noise) is standard normally distributed. On the first one I am completely lost but would the expected value of the second and third be 0, since the expected value of error term sum to 0, and variance just sigma squared because we only have the error terms in the model? Help with how to find both for the first one will be appreciated.
$$Y_t=Y_{t-1}+\epsilon_t$$ $$Y_t=\epsilon_t-\epsilon_{t-1}+\epsilon_{t-2}$$ $$Y_t=-\sum_{j=1}^t\epsilon_j$$