Answer:

Adding one more student increased the time spent on homework by eight minutes each time.

TEACHER NOTES:
Students should have opportunities to study situations representing different patterns of change—change that occurs at a constant rate, such as someone walking at a constant speed, and change that occurs at an increasing or decreasing rate, as in a growing plant.7

7 National Council of Teachers of Mathematics. (2000). Principles and standards for school mathematics. Reston, VA: Author.