a$.$ Demand forecast can be made at different levels $($e$.$g$.,$ book level, demand center level, and item level$).$ How do you rank the accuracy of the demand forecasts at these three different levels? State your reason.

b$.$ In the first paragraph of page $4,$ Barbara mentioned that if the sum of the item forecasts of a catalog was at variance with the dollar target for that book, then usually the item forecasts would be adjusted according to the book forecast. Why don$$t they do it the other way round $($adjust the book forecast according to sum of item forecasts$)?$ Hint: the answer follows directly from part a$.$