An ideal mixture of two liquids A and B is put in a cylinder containing a piston. The piston is pulled out isothermally so that the volume of liquid decreases but that of vapours increases. Negligibly small amount of liquid was left and mole fraction of A in vapour is 0.4. If $P^\circ_A = 0.4$ atm and $P^\circ_B = 1.2$ atm at the experimental temperature, which of the following is the total pressure at which the liquid is almost evaporated?