This resource comes from OER commons. https://tasks.illustrativemathematics.org/content-standards/8/G/B/8/tasks/1919

This activity has students determine the slope between ordered pairs. The last set of ordered pairs are variables instead of numbers.

I would use this activity after the students have learned the distance formula and after they have practiced using the distance formula on IXL- https://www.ixl.com/math/geometry/distance-formula (students can answer 10 questions per day as a guest).