If ABC - ADEF, find the length EF. A D 8 24 3 6

We have similar triangles. we can use the ratio of proportional sides to find the missing sides
AB DE
----- = --------
BC EF
8 24
---- = ------
6 EF
Using cross products
8 * EF = 24*6
Divide each side by 8
ER = 24*6/8
EF =18