Find the Derivative of the Function at P0 in the Direction

Multiple Choice

Find the derivative of the function at P0 in the direction of u.
- $$f ( x , y , z ) = 4 x + 8 y - 7 z , \quad P _ { 0 } ( - 7,10 , - 10 ) , \quad \mathbf { u } = 3 \mathbf { i } - 6 \mathbf { j } - 2 \mathbf { k }$$

A) $\frac { 2 } { 7 }$
B) $\frac { 10 } { 7 }$
C) $- \frac { 46 } { 7 }$
D) $- \frac { 22 } { 7 }$