Two liquids \( A \) and \( B \) form an ideal solution. At \( 320 \, \text{K} \), the vapour pressure of the solution, containing \( 3 \) mol of \( A \) and \( 1 \) mol of \( B \) is \( 500 \, \text{mm Hg} \). At the same temperature, if \( 1 \) mol of \( A \) is further added to this solution, vapour pressure of the solution increases by \( 20 \, \text{mm Hg} \). Vapour pressure \( \)(in mm Hg\( \)) of \( B \) in pure state is _________ \( \). \( \)(Nearest integer\( \))
