What is the area of the shape below?

The depth of a lake at a certain point, wich is a function of the distance of that point from shore, is 30 feet.

Jackie purchased 3 bottles of water and 2 cups of coffee for the family for $7.35. ryan bought 4 bottles of water and 1 cup of coffee for his family for 7.15. how much does each bottle of water cost? how much does each cup of coffee cost?

What is the average rate of change for this function for the interval from x=2 to x=4 ?