The Absolute Maximum Of $f ( x , y ) = x ^ { 2 } + y ^ { 2 } + x y - 6 x$

Multiple Choice

The absolute maximum of $f ( x , y ) = x ^ { 2 } + y ^ { 2 } + x y - 6 x$ on or inside the rectangle with vertices (0, -3) , (5, -3) , (5, 3) , and (0, 3) is

A) 19
B) 16
C) 14
D) 12
E) 8