$(7)$ Consider a Diffie$-$Hellman scheme with a common prime $q=11$ and a primitive root $a=2$

a$.$ If user A has public key $Y_A=10$ what is A$\text{'}$s private key $x_A?$

b$.$ If user $B$ has public key $Y_B=5,$ what is the shared secret key $K?$