What Is the Value of K_b for the Cyanide Anion,CN^- $\times$

What is the value of K_b for the cyanide anion,CN^-?
K_a(HCN) = 6.2 $\times$ 10^-10

A) 1.6 $\times$ 10^-4
B) 1.6 $\times$ 10^-5
C) 3.8 $\times$ 10^-4
D) 3.8 $\times$ 10^-5
E) 6.2 $\times$ 10⁴