What is half of 2.1 cm

Use set builder notation to represent the following set: { -3, -2, -1, 0}

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?

17 in long 1.3 ft wide and 8in high what is the volume