How do you do it? how do you start and get the answer

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

Gabrielle's age is two times mikhail's age. the sum of their ages is 84. what is mikhail's age?

Find the percent error of the measurement 4 cm