Use square roots to solve the equation x^2= -625

What number must you add to complete the square x^2+12x=16

Hi my sisters and brothers can tell me the answer because i don’t understand the question

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?