A monoprotic weak acid, HA, dissociates in water according to the reaction:
HA(aq) + H2O(l) ⇌ H3O+(aq) + A-(aq)
The equilibrium concentrations of the reactants and products are [HA] = 0.130 M; [H3O+] = 3.00 x 10^-4 M, and [A-] = 3.00 x 10^-4 M. Calculate the Ka value for the acid HA.