A flask contains a mixture of compounds $\mathrm{A}$ and $\mathrm{B}$. Both compounds decompose by first-order kinetics. The half-lives for $\mathrm{A}$ and $\mathrm{B}$ are $300 \mathrm{s}$ and $180 \mathrm{s}$, respectively. If the concentrations of $\mathrm{A}$ and $\mathrm{B}$ are equal initially, the time required for the concentration of A to be four times that of $\mathrm{B}$ (in s) is : $(\mathrm{Use} \ln 2=0.693)$