This question is basically asking "what factor pairs (pairs of numbers multiplied together) make 18?"
I don't know anything about your board, so some of these might not be possible. (Maybe yours doesn't go all the way up to 18--just be sure to check yourself on it.)
1 × 18
2 × 9
3 × 6
6 × 3
9 × 2
18 × 1
