Factors of 80:
1 x 80 [ Difference is 79]
2 x 40 [Difference is 38]
4 x 20 [Difference is 16]
5 x 16 [Difference is 11]
8 x 10 [Difference is 2]
From the information above, we can conclude that the length is 16 and the width is 5, which gives us a difference if 11.