$2(50$ points$).$ Find the directional Derivative:

$f(x,y,z)=xyyzxz$ at $(x_0,y_0,z_0)=(1,-1,2),$ in the direction of $V=3i6j-2k.$

Choose the right answer from the following possible answers:

a$.$

$D_{A}f=2$

b$.$

$D_{A}f=5$

c$.$

$D_{A}f=3$

d$.$

None of the above