$12\mathrm{.}1\mathrm{.}6$ The electric power consumed each month by a chemical plant is thought to be related to the average ambient temperature $(x_1),$ the number of days in the month $(x_2),$ the average product purity $(x_3),$ and the tons of product produced $(x_4).$ The past year's historical data are available and are presented below.

$\backslash$table$[[y,x_1,x_2,x_3,x_4$