When a simple reversible reaction, $AB($in which both the forward and reverse reactions are first$-$order$)$ is run with initial concentrations $[A{]}_0=0\mathrm{.}200M$ and $[B{]}_0=0,$ the initial rate of disappearance of $A$ is $5\mathrm{.}30{10}^{-3}\frac{M}{s},$ and the final $($equilibrium$)$ concentration of $A$ is $0\mathrm{.}135M.$ a$)$ Calculate the values of $K_c$ and $k_{eq}$ for this reaction. b$)$ How long does it take $[$A$]$ to fall from $0\mathrm{.}200M$ to $0\mathrm{.}150M$ in this case?