Data for length of the tail (in millimeters) and age (in days) of tadpoles is entered into a statistics software package and results in a regression equation of = 15 - 1.5x.

What is the correct interpretation of the slope if the length of the tail is the response variable and the age is the explanatory variable?

• The length of the tail decreases by 1.5 millimeters, on average, when the tadpole's age increases by 1 day.
• The length of the tail increases by 1.5 millimeters, on average, when the tadpole's age increases by 1 day.
• The length of the tail increases by 15 millimeters, on average, when the tadpole's age increases by 1 day.
• The length of the tail decreases by 15 millimeters, on average, when the tadpole's age increases by 1 day.