x = 2t, y = –4t, z = 4t

so  

$\mathrm{t}=\frac{\mathrm{x}}{2},\mathrm{t}=\frac{\mathrm{y}}{-4},\mathrm{t}=\frac{\mathrm{z}}{4}\Rightarrow \frac{\mathrm{x}}{2}=-\frac{\mathrm{y}}{4}=\frac{\mathrm{z}}{4}$

So path is a straight line, & pass through origin, as it (0,0,0)

Now 

At t = 10

x = 2t = 20, y = –4(t) =–40

$\left|\overrightarrow{\mathrm{r}}\right|=\sqrt{(\mathrm{x}-0{)}^2+(\mathrm{y}-0{)}^2+(\mathrm{z}-0{)}^2}$

$=\sqrt{{20}^2+(-40{)}^2+(40{)}^2}$

$=\sqrt{400+1600+1600}$

Hence, Distance = 60km.