Managerial accounting

need questions answered in 4-6 sentences.
TEXT: Accounting: Text and Cases, 12th Edition. Robert N. Anthony, David F. Hawkins, and Kenneth A. Merchant, McGraw-Hill.
7. What are some of the benefits of a well-prepared budget?
8. Why are fixed costs generally more relevant in long-run decisions than short-run decisions?
9. Why is depreciation expense irrelevant to most managerial decisions, even when it is a future cost?
10. Under what circumstances is the sum of variable production and selling costs the appropriate minimum price for special orders?