The monthly cost (in dollars) of water use is a linear function of the amount of water used (in hundreds of cubic feet, hcf). the cost for using 18 hcf of water is $38.98 , and the cost for using 29 hcf is $58.23 . what is the cost for using 23 hcf of water?
y = mx + b slope(m) = 1.75 use either of ur points...(18,38.98)...x = 18 and y = 38.98 now sub and find b, the y int 38.98 = 1.75(18) + b 38.98 = 31.5 + b 38.98 - 31.5 = b 7.48 = b so ur equation is : y = 1.75x + 7.48...where x is the amount of water used and y is the monthly cost
so the cost for 23 hcf.....sub in 23 for x y = 1.75x + 7.48 y = 1.75(23) + 7.48 y = 40.25 + 7.48 y = $ 47.73 <===== ur answer
