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Niagara Electric charges a flat fee of $8.50 for the first 1000 kilowatt hours used, $0.05 per kilowatt hour for the next 4000 kilowatt hours, and $.04 per kilowatt hour for each hour used thereafter. What is the expression for the cost function, C(x), using standard notation?
I think you need two expression
x =< 5000 kwh
C(x) = .05(x-1000) + 8.50
x > 5000 kwh,(add 1 cent per kwh for 4000 kwh)
C(x) = .04(x-1000) + 40.00 + 8.50
C(x) = .04(x-1000) + 48.50