2. Consider the function \\
$\phi(x, y, z) = xy + yz + xz.$ \\
(a) Find its rate of change in the direction $(1, 2, 3)$ at the point \\
$(1, 3, -1)$. \\
(b) At this same point, $(1, 3, -1)$, find the rate of change in the direction in which $\phi$ increases the most rapidly.