\[begin{array}{l} {\text{Units of production depreciation}}\ = \frac{{{\text{Original cost - salvage value}}}}{{{\text{life in output units}}}}{\text{Output units in the period}} end{array}\]
\[Effective{\text{ }}tax{\text{ }}rate = \frac{{Income{\text{ }}tax{\text{ }}expense}}{{Pretax{\text{ }}income}}\]