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Evaluate the expression for the given value of the variable 2×(c2-5) for c=4

Suppose that a households monthly water bill (in dollars) is a linear function of the amount of water the household uses (in hundreds of cubic feet, hcf). when graphed, the function gives a line with slope of 1.65. if the monthly cost for 13 hcf is $46.10 what is the monthly cost for 19 hcf?

If a is a nonzero real number then the reciprocal of a is