A family pays 12 cents per kilowatt-hour of energy it consumes, along with a $15 service charge. Thus, its monthly energy cost, in dollars, is given by the function C(x)=15 + 0.12x, where x is the amount of energy, in kilowatt-hours, it uses per month. a. Show that the formula C(x) = 123 + 0.12(x-900) is equivalent to the given formula. What form of a linear function is this formula (slope-intercept, point-slope, or standard form)? b. Find the monthly energy cost of a home that uses 910 kilowatt-hours of energy per month. c. Given that average household energy consumption is approximately 900 kilowatt-hours per month, explain why the formula given in part (a.) might be more useful for computing household energy costs than the original formula. d. Write a formula for C(x) that might be useful for a family that uses around 1200 kilowatt-hours each month.