How many lbs. of walnuts which cost $7/lb must be added to 4 lbs of peanuts which cost $10/lb to make mixed nuts which cost $9/lb

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?