You can split up the length of AE into the lengths of the line segments connecting adjacent points:
AE = AB + BC + CD + DE
Plug in everything you know and solve for DE :
9 = (2 1/2) + (4 1/3) + (1 2/3) + DE
Rewrite the mixed numbers as improper fractions with a common denominator.
2 1/2 = 4/2 + 1/2 = 5/2 = 15/6
4 1/3 = 12/3 + 1/3 = 13/3 = 26/6
1 2/3 = 3/3 + 2/3 = 5/3 = 10/6
9 = 54/6
So we have
54/6 = 15/6 + 26/6 + 10/6 + DE
⇒ DE = (54 - 15 - 26 - 10)/6 = 3/6 = 1/2
(It looks as though you will need to enter 1 in the top box and 2 in the bottom one)