at At a certain temperature, the equilibrium constant for the chemical reaction shown is $1\mathrm{.}39{10}^{-3}.$ At equilibrium, the concentration of $AB$ is $1\mathrm{.}825M,$ the concentration of $BC$ is $3\mathrm{.}125M,$ and the concentration of $AC$ is $0\mathrm{.}140M.$ Calculate the concentration of $B$ at equilibrium.

$AB(aq)+BC(aq)AC(aq)+2B(aq)$