The accompanying data set contains two predictor variables, x₁ and x₂, and one numerical target variable, y. A regression tree will be constructed using the data set.

a. Which split on x₁ will generate the smallest MSE?
b. Which split on x₂ will generate the smallest MSE?
c. Which variable and split value should be used to create the root node if a regression tree is constructed using the accompanying data set?
d. State the rules generated from this split.