You're more likely to get a reply if you include a screen shot of the question and solution (as well as including the topic area covered in the title)- as otherwise students have no idea what the question is about and then have to look it up before they can answer. We have: \((1-0.4B)Y_t = (0.1+0.9e_{t-1}+e_t)\) So we multiply both sides by the inverse of \((1-0.4B)\): \(Y_t = (1-0.4B)^{-1}(0.1+0.9e_{t-1}+e_t)\) We can then use a series expansion on the \((1-0.4B)^{-1}\) part using the formula given on page 2 of the Tables.
