In the titration of a solution of a weak base `BOH` with HCI has `pH` is `8.2` after `10 ml` of HCI solution has been added and 7.6 after 20 ml of HCI solution has been added. Calculate the value of `pK_(b)` of the base and express your answer as ab.cd [For example if your answer is 3.8 then write answer as 0380]
[Given : log `2 = 0.3`]