Help me i’m stuck and this is due tomorrow

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?

Ming says that 0.24 > 1/4 because 0.24= 2/4. which best explains mings error

Which of the following equations is equivalent to x/3-6/x=1