For the Regression Equation $=20+8 x_{1}+5 x_{2}+3 x_{1} x_{2}$ , Which Combination Of

Multiple Choice

For the regression equation $=20+8 x_{1}+5 x_{2}+3 x_{1} x_{2}$ , which combination of $x _ { 1 }$ and $x _ { 2 }$ , respectively, results in the largest average value of y?

A) 3 and 5.
B) 5 and 3.
C) 6 and 3.
D) 3 and 6.