The regression line μy = 31 + 5.5x models the relationship for students in one math class between hours studied for a test (x) and score on the test (y). The conditional distribution of y at each value of x is modeled as normal, with σ = 8.1. Use this regression model to describe the mean and the variability around the mean for the conditional distribution for a study time of 6.4 hours. Please help me better understand this example.