How do i solve this by substitution?

Jackie purchased 3 bottles of water and 2 cups of coffee for a family for $7.35. brian 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? i need this done

Write the rational number in lowest terms 99/-15

How many sides does a regular polygon have if each exterior angle measure is 45 degrees explain your answer, i really don't understand this.