Answer: That Y increases by 20 units for each unit increase in X.
The value of 20 in the least squares equation Ŷ = 10 + 20X indicates that for each unit increase in X, the predicted value of Y (Ŷ) increases by 20 units. This means that the relationship between X and Y is such that for every one unit increase in X, the predicted value of Y will increase by 20 units. So, the correct answer is: "That Y increases by 20 units for each unit increase in X."