Answer:
 (c)  Segment BD = 15
Step-by-step explanation:
You have ∆ABC with ∆DEF inscribed so that DE║BC, EF║AB, and points D, E, and F lie on segments AB, AC, and BC, respectively. You want to know the lengths of BF and BD, given that AD=18, AE=24, EC=20, FC=30.
The parallel lines divide the triangle sides proportionally, so we have ...
 BD/AD = CE/AE
 BD/18 = 20/24 . . . . . using the given values
 BD = 18(20/24) = 15
On the other side, we have ...
 BF/CF = AE/CE
 BF/30 = 24/20
 BF = 30(24/20) = 36 . . . . . not among the answer choices
The length of interest is ...
 Segment BD = 15.