How many gallons of 20 % alcohol solution and 35 % alcohol solution must be mixed to get 9 gallons of 25 % alcohol solution?

Just tell me how to set up the equation.

What are the solutions of the system? solve by graphing. y = x^2 + 3x + 2 y = 2x + 2

Last month, a 770 g box of cereal was sold at a grocery store for $3.10. however, this month, the cereal manufacturer launched the same cereal in a 640 g box, which is being sold at $2.50. what is the percent change in the unit price?