To mix mortar to lay bricks, you need 2.5Kg of cement,4kg of sand and 3 liters of water. Sand is sold in 10kg bags. How much cement and water will I need to add to make mortar?

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?