Find the Directional Derivative Of $f ( x , y ) = 2 \sqrt { x } - y ^ { 3 }$

Multiple Choice

Find the directional derivative of $f ( x , y ) = 2 \sqrt { x } - y ^ { 3 }$ at the point (1, 3) in the direction toward the point (3, 1) . Select the correct answer.

A) $7 \sqrt { 2 }$
B) $14 \sqrt { 2 }$
C) $\sqrt { 2 }$
D) 28
E) none of these