15.1 The predicted humerus length for a fossil with a femur 70 cm long is

humerus length = −3.66 + (1.197)(70) = 80.13 cm

15.2 The proportion of the variation in hot dog prices explained by the least-squares regression of hot dog prices on beer prices (per ounce) is r² = (0.36)² = 0.1296 or 12.96%.

15.3 The observed relationship is certainly not direct causation. Some confounding is possible (food prices may be somewhat standardized at a baseball stadium), but the correlation is most likely due to common response: prices for food and beer probably depend on general economic trends.