Answer:
Segment BF = 16 is true.
Step-by-step explanation:
Since, DE is parallel to BC, so DE will divide AB and AC proportionally.
Hence,

⇒
{Since, given that AE = 12, EC = 18 and AD = 6}
⇒ BD = 9.
Again, since, EF is parallel to AB, so EF will divide BC and AC proportionally.
Hence, 
⇒
{Since, given that AE = 12, EC = 18 and FC= 24}
⇒ BF = 16.
Therefore, segment BF = 16 is true. (Answer)
In a triangle, the nomenclature is that a variable side a is opposite of the angle A. we can use the cosine law to determine the value of cosine A.
a2 = b2 + c2 -2bc cos a25 = 36 + 64 - 2*6*8 * cos acos a = 25/32