The answer is C. (2jk)^-2
Answer with Step-by-step explanation:
Let F be a field .Suppose
and 
We have to prove that a has unique multiplicative inverse.
Suppose a has two inverses b and c
Then,
where 1 =Multiplicative identity

(cancel a on both sides)
Hence, a has unique multiplicative inverse.
Answer:
The mean depends on the no. of family members but the question hasn't mentioned it. So I have no idea what to do with this.