Please answer the given financial question based on the context.
Context: entergy gulf states louisiana , l.l.c . management 2019s financial discussion and analysis plan to spin off the utility 2019s transmission business see the 201cplan to spin off the utility 2019s transmission business 201d section of entergy corporation and subsidiaries management 2019s financial discussion and analysis for a discussion of this matter , including the planned retirement of debt and preferred securities . results of operations net income 2011 compared to 2010 net income increased $ 12.3 million primarily due to lower interest expense and lower other operation and maintenance expenses , offset by higher depreciation and amortization expenses and a higher effective income tax 2010 compared to 2009 net income increased $ 37.7 million primarily due to higher net revenue , a lower effective income tax rate , and lower interest expense , offset by higher other operation and maintenance expenses , lower other income , and higher taxes other than income taxes . net revenue 2011 compared to 2010 net revenue consists of operating revenues net of : 1 ) fuel , fuel-related expenses , and gas purchased for resale , 2 ) purchased power expenses , and 3 ) other regulatory credits . following is an analysis of the change in net revenue comparing 2011 to 2010 . amount ( in millions ) .
||amount ( in millions )|
|2010 net revenue|$ 933.6|
|retail electric price|-20.1 ( 20.1 )|
|volume/weather|-5.2 ( 5.2 )|
|fuel recovery|14.8|
|transmission revenue|12.4|
|other|-2.1 ( 2.1 )|
|2011 net revenue|$ 933.4|
the retail electric price variance is primarily due to an increase in credits passed on to customers as a result of the act 55 storm cost financing . see 201cmanagement 2019s financial discussion and analysis 2013 hurricane gustav and hurricane ike 201d and note 2 to the financial statements for a discussion of the act 55 storm cost financing . the volume/weather variance is primarily due to less favorable weather on the residential sector as well as the unbilled sales period . the decrease was partially offset by an increase of 62 gwh , or 0.3% ( 0.3 % ) , in billed electricity usage , primarily due to increased consumption by an industrial customer as a result of the customer 2019s cogeneration outage and the addition of a new production unit by the industrial customer . the fuel recovery variance resulted primarily from an adjustment to deferred fuel costs in 2010 . see note 2 to the financial statements for a discussion of fuel recovery. .
Question: by what percentage point did the net income margin improve in 2010?


Answer: The answer is:0.04038