Here's a breakdown:

* Kb is the base dissociation constant, which measures the strength of a base in solution. A higher Kb value indicates a stronger base.

* CH3NH2 is the formula for methylamine, a weak base.

* H2O is water, which acts as a solvent in this reaction.

* CH3NH3+ is the methylammonium ion, the conjugate acid of methylamine.

* OH- is the hydroxide ion, a product of the base dissociation reaction.

The reaction in question is:

CH3NH2(aq) + H2O(l) ⇌ CH3NH3+(aq) + OH-(aq)

You can find the Kb value for methylamine in tables of common acid and base dissociation constants.