Let A be the foot of the origin on the line L :  $\frac{x-9}{1}=\frac{y}{2}=\frac{z}{-2}$  and B be the point (12, 2, 2) then the length of the projection of $\overline{AB}$  on the line ‘L’ is equal to

A = (t + 9, 2t, -2t) and DRs of L are (1, 2, -2) and $\overline{OA}\perp L$

$\Rightarrow \left(1\right)\left(t+9\right)+\left(2\right)\left(2t\right)+\left(-2\right)\left(-2t\right)=0\Rightarrow t=-1$

$\therefore A^1=\left(8,-2,2\right),B=\left(12,2,2\right)\Rightarrow DrsofABare\left(4,4,0\right)$

Projection of AB on $L=\left[\frac{\left(1\right)\left(4\right)+\left(2\right)\left(4\right)+\left(-2\right)\left(0\right)}{\sqrt{1+4+4}}\right]=4$