A researcher studies the relationship between the number of hours of sleep per night and the performance on a memory test. Study participants are randomly selected to get no sleep or sleep in 1-hour increments, up to 8 hours total (that is, the participant gets 1 hour, 2 hours, and so on, up to 8 hours of sleep). The researcher determines that the association between the two variables can be modeled with the linear equation p = 9h + 15, where h is number of hours of sleep and p is the percentage score on the memory test. Use the slope in the equation to describe the association between the hours of sleep and the performance on the memory test.​