Cocaine is a weak base, and the aqueous ionization can be indicated as:

C(aq) + H2O ≡ CH+(aq) + -
OH(aq)
In a 0.0040 M solution of cocaine, the ratio of -
OH(aq) ions to cocaine molecules is 1.0/120.
What is the value of Kb for cocaine?

See your other post much later. I solved it there.