The answer would be length is 6, and width would be 3.
How to find the answer:
First you make combinations that multiply to 18 (because area is length times width)
2 x 9
3 x 6
6 x 3
9 x 2
since the last two are basically the same as the first two, you can get rid of those.
2 x 9
3 x 6
since 3 is half of 6 (and 2 isn't half of 9),
3 x 6 is the answer.
Hope this helps.
