Edward C. answered 03/09/15
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Caltech Grad for math tutoring: Algebra through Calculus
Let K = consumption in kWh
The total bill of $104.60 is equal to a fixed charge of $20 plus 9 cents for each K. So the equation is
104.60 = 20 + .09*K
84.60 = .09*K
K = 84.60/.09 = 940
So the consumption was 940 kWh
Check: 20 + .09*(940) = 20 + 84.6 = 104.60