The answer is <span>20.3896551724</span>
Assuming T, B and N are all on the same line, then we can say
BT + TN = BN
which is the segment addition postulate.
Subtract TN from both sides to get
BT + TN = BN
BT + TN - TN = BN - TN
BT = BN - TN
BN - TN = BT
Which is what choice C is saying. Therefore the answer is choice C.
