What sides are these two triangles?

Consider the function represented by the equation 1/2 j + 1/4 k equals 3 which shows the equation written in function notation with j as the independent variable

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?

Use sigma notation to represent the following series for 9 terms.