This is to help introduce slope for the first time based on the fact that students have previous knowledge of proportional relationships. It helps them to understand that slope is the same thing as unit rate, the rate of change, and constant of proportionality. They will then brainstorm where slope is used in real life.
I used it in my 8th grade classroom to introduce slope. Previously in 7th grade, students have learned about proportional relationships and mastered the concept of unit rate.