How do you turn these in to an inequality

Two lines parallel to the same plane are parallel to eachother

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?

Can someone me with my math problems i have a bunch. i will give brainliest and lots of pleeeaaasssee