What is the unit vector in the same direction as u = (6, 8)?

A unit vector in the same direction divides the vector by its magnitude. The magnitude of $(6,8)$ is $\sqrt{6^2+8^2}=\sqrt{100}=10$. Dividing each component by $10$ gives $(0.6,0.8)$, choice D. Check: $0.6^2+0.8^2=0.36+0.64=1$. Choice A, $(3,4)$, divides by $2$ and has magnitude $5$. Choice B is the original vector with magnitude $10$. Choice C, $(0.06,0.08)$, divides by $100$, which is the magnitude squared, and has magnitude $0.1$. Only choice D has length exactly $1$.