The OH^$-$ concentration in a mixture of 5.0 mL of 0.0504 M NH₄Cl and 2 mL of 0.0210 M NH₃ solution is x $\times$ 10^$-$6 M. The value of x is ___________. (Nearest integer)

[Given K_w = 1 $\times$ 10^$-$14 and K_b = 1.8 $\times$ 10^$-$5]