A) In similar figures (not just in similar triangles), lengths between corresponding sides/height/etc can be expressed in a ratio I.E 1:2 for height of drill bit hole to drill bit and 2:3 for stuck drill bit to complete drill bit. So volume between similar figures would be the cube of the above ratios.

1/3 of the height of the drill bit hole is stuck since 4/6 (2/3) of the stuck height of comp drill bit would cover 1/3 of the height. (From 1:2)