At 298k the base dissociating constant Kb of CH3NH2 is 4.5×10mol/dm

Question

Write an expression for the kb of CH3NH2

Answer 1

I think you omitted the exponent for the Kb but that isn't needed in order to write the Kb expression.
CH3NH2 + HOH ==> CH3NH3^+ + OH^-
Kb = (CH3NH3^+)(OH^-)/(CH3NH2)