Solve the equation
show your work
9 + 12m = 6 + 15(m - 1)

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?

What is always true when two whole numbers are subtracted?

Ihonestly have no clue if it's each or none.