There is only one answer you could pick. You need something that is divisible into 14 which is either 2 or 7. There's a 2 in a, but 5 doesn't divide into either 36 or 18. So A is out.
The only answer possible is 7 (which goes into 14 so you could get 2 containers going in the 14 direction) 9 which means you could get 2 containers going in the 18 direction, and 9 which would let you get 4 containers going in the 36 direction. The wording is just a little strange, but the way I've written it is what is meant.
