Convert these into proper fractions into mix number 8 /5

With #! i’ve tried to figure it out but i can’t.

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?

Cos^2x+cos^2(120°+x)+cos^2(120°-x)i need this asap. pls me