Concept:
Direction vector = difference of points.
Step 1: Find direction vector.
\[
\vec{d} = (13-10, 9-8, 4-6) = (3,1,-2)
\]
Step 2: Find magnitude.
\[
|\vec{d}| = \sqrt{9 + 1 + 4} = \sqrt{14}
\]
Step 3: Unit vector.
\[
\frac{1}{\sqrt{14}}(3\hat{i} + \hat{j} - 2\hat{k})
\]