Electrochemistry Part 2

Consider the following electrochemical cell at standard condition.
‌Au( s)‌|QH2,Q|‌NH4‌X(0.01M)||Ag+(1M)∣Ag( s)
‌E‌cell ‌=+0.4V The couple QH2∕Q represents quinhydrone electrode, the half cell reaction is given below :[‌ Given ‌:EAg+∕Ag∘=+0.8V‌ and ‌‌

2.303‌RT

F

=0.06V]
The pKb value of the ammonium halide salt ( NH4X ) used here is _______ . (nearest integer)