Identify the missing number in the given series

6,  6,  6.5,  5.5,  7,  4.5,  7.5,  3,  8, ____

P is the brother of Q and R. S is R’s mother. T is P’s father. How many of the following statements are definitely true?

1.  S and T are a couple.
2.  Q is T’s son.
3.  T is Q’s father. 
4.  S is P’s mother.
5.  R is T’s daughter.
6.  P is S’s son.

In a certain coding language, If the word MASTER  is coded as 15Y21R7P, then what it the code for SACHIN?

Identify the missing term in the given Series

BU, GS, LQ, QO, _____, AK