how to use the pythagorean theorem on a rectangle that is missing a side and its represented by a letter?

Which expression is equivalent to (3^2)^-2 a.-81 b.-12 c.1/81 d.1/12

All per-unit concepts rely on ratios,meaning,to provide a type of measurement

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?