Why would negative numbers not make sense for the values of the variables

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?

Three times the sum of a number and seven is negative thirty-six. what is the number?

Joanie wrote a letter that was 1 1/4 pages long. katie wrote a letter that was 3/4 page shorter then joagies letter. how long was katies letter