Can someone please help me with this problem? I tried but didnt get the correct answer. Thank you!!!!!!

A mixture having a vol of 0.01 L and containing 0.1 M Ag+ and 0.1 M Hg2+ was titrated with 0.1 M KCN to precipitate Hg2(CN)2 and AgCN.
a) cal pCN- at each of the following volumes of added KCN: 5.0mL, 10.00 mL, 15.00 mL
b) should any AgCN be precipitated at 19.90 mL?

For a) here is what I did:
moles of Hg2 : .01 L * .1 M = .005L * .1 M and got 5.0 *10^-4
[Hg2+] = 5.0 *10^-4/0.015 L = 1.50 * 10^-38
pCN- = -log(1.50 * 10^-38 ) = 37 which is incorrect. The correct answer should be 19