(a) The tax impact of each line item was calculated using Avista Corp.'s statutory tax rate (federal and state combined) of 23.05 percent. (b) Electric utility margin (operating revenues less resource costs) increased for the fourth quarter and full year and was impacted primarily by the following: General rate increase in Washington, effective April 1, 2020. Customer growth contributed additional retail electric revenue A decrease in net power supply costs caused by a decrease in power purchased prices and thermal fuel costs for the full year 2020 when compared to 2019. For the full year 2020, we recognized a pre-tax benefit of $6.2 million under the Energy Recovery Mechanism (ERM) compared to a pre-tax benefit of $4.4 million for the full year 2019.