What is the distance between (6, 8, 2)  and (0, 6, 0) ?

The distance is $6.633$.
The distance between two points $\left({x}_{1} , {y}_{1} , {z}_{1}\right)$ and $\left({x}_{2} , {y}_{2} , {z}_{2}\right)$ is $\sqrt{{\left({x}_{2} - {x}_{1}\right)}^{2} + {\left({y}_{2} - {y}_{1}\right)}^{2} + {\left({z}_{2} - {z}_{1}\right)}^{2}}$.
Hence distance between $\left(6 , 8 , 2\right)$ and $\left(0 , 6 , 0\right)$ is $\sqrt{{\left(0 - 6\right)}^{2} + {\left(6 - 8\right)}^{2} + {\left(0 - 2\right)}^{2}}$ or
$\sqrt{{\left(- 6\right)}^{2} + {\left(- 2\right)}^{2} + {\left(- 2\right)}^{2}} = \sqrt{36 + 4 + 4} = \sqrt{44} = 6.633$