Answer:
6 dm
Step-by-step explanation:
Triangle DBE is similar to triangle ABC, so their side lengths are proportional.
DE/AC = DB/AB
The length of DB can be found from ...
DB +AD = AB
DB = AB -AD = (15 -10) dm = 5 dm
So, we can fill in the proportion:
DE/(18 dm) = (5 dm)/(15 dm)
DE = (18 dm)·(1/3) . . . . . . . . . . simplify, multiply by 18 dm
DE = 6 dm
_____
It can be helpful to draw and label a figure.
