If two substances A and B have = 1 : 2and have mole fraction in solution 1 : 2, then mole fraction of A in vapours is

According to  Raoult's law,    Ptot=PA+PB           Where  PA,PB   = V.P of  components A & B in a mixture                                                                                               XA, XB = M.F of  components in liquid phase According to Dalton's law,                               PA = Ptot YA        ;      PB = PtotYBYA , YB = M.F of components in vapour phaseGiven,   = 1:2             XA:XB = 1:2         YA =?     ;     YB =4 YAYA+YB = 15YA = 1YA = 0.2