What is the domain and range of this

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?

Find the domain of the following expression: 1/(√x)-2

Another type of subtraction equation is 16-b=7. explain how you would sole this equation then solve it.