I've been trying to solve these for while now, and i keep getting them wrong.... please help!!

Question

A solution of NH4Cl hydrolyzes according to the equation. If the [NH3] in the solution after hydrolysis is 0.00000508 M, calculate the equilibrium concentration of NH4Cl.

NH4+(aq) + H2O(l) = H3O+(aq) + NH3(aq)

and....

The base dissociation equilibrium constant (Kb) for NH2OH is 1.10×10-8 (eq. 1).

(eq. 1): NH2OH(aq) + H2O(l) = OH-(aq) + HONH3+(aq)

Calculate the value of the equilibrium constant (Ka) for the hydrolysis of HONH3+ as shown in the reaction (eq. 2).

(eq. 2): HONH3+(aq) + H2O(l) = H3O+(aq) + NH2OH(aq)