Dissociation constant of ${\mathrm{H}}_2\mathrm{O}$ at $25°\mathrm{C}$ is:

${\mathrm{K}}_{\mathrm{a}}$ value for the acid $\mathrm{HA}$ is $1\times {10}^{-6}$.  The value of $\mathrm{K}$ for the reaction, ${\mathrm{A}}^{-}+{\mathrm{H}}_3{\mathrm{O}}^{+}\leftrightharpoons \mathrm{HA}+{\mathrm{H}}_2\mathrm{O}$ is

What molar concentration of ${\mathrm{NH}}_3$ provides a $\left[{\mathrm{OH}}^{-}\right]$ of $1.5\times {10}^{-3}$? $\left({\mathrm{K}}_{\mathrm{b}}=1.8\times {10}^{-5}\right)$