$1.$ In a chemical equilibrium system, the concentration of $\backslash ($ A $\backslash )$ is $0\mathrm{.}8$ M$,\backslash ($ B $\backslash )$ is $1\mathrm{.}2$ M$,$ and the equilibrium constant $\backslash ($ K$\_$c $\backslash )$ is $4.$ Calculate the concentration of $\backslash ($ C $\backslash ).$