Desribe the dilation of a line segment by a scale factor of 1/2 centered at the origin

Hi, can anyone show me how to do this problem? 100 points for this. in advance

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?

98 point question what is the record for most points in one