Use the Gradient to Find the Directional Derivative of the Function

Multiple Choice

Use the gradient to find the directional derivative of the function at P in the direction of Q. $f ( x , y ) = \sin ( 7 x ) \cos y , P ( 0,0 ) , Q \left( \frac { \pi } { 7 } , \pi \right)$

A) $\pi$
B) $\pi ( \sin ( 7 x ) \cos y + \cos ( 7 x ) \sin y )$
C) $\pi ( \cos ( 7 x ) \cos y - \sin ( 7 x ) \sin y )$
D) $\frac { 1 } { \sqrt { 50 } }$
E) $\frac { 7 } { \sqrt { 50 } }$