Well, we should start by listing the factors
1,2,3,4,6,8,9,12,16,24,36,72
You can put these in pairs if it will help you,
1*72 2*36 3*24 4*16 6*12 8*9
If you look, you can see that in only one pair the length is twice the width.
So your answer is
W=6
L=12
