Using proportions, it is found that the estimate of the the per capita consumption from 2011 was of 29.25 gallons.
A proportion is a fraction of a total amount, and the measures are related using a rule of three.
The amount in 2012 was a increase of 5.3% from 2011, that is, 105.3% = 1.053 of x, and the consumption per capita was of 30.8 gallons, hence:
1.053x = 30.8
x = 30.8/1.053
x = 29.25 gallons.
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