A flask is filled with equal moles of \( A \) and \( B \). The half lives of \( A \) and \( B \) are \( 100 \, \text{s} \) and \( 50 \, \text{s} \) respectively and are independent of the initial concentration. The time required for the concentration of \( A \) to be four times that of \( B \) is ____________ \( \text{s} \). (Given: \( \ln 2 = 0.693 \))