Raoul's Law: $-100$ gm of Liquid A $($Mwt$=140$ g$/$mole$)$ was mixed with $100$ gm of Liquid B $($Mwt$=180$ g$/$mole$).$ The vapor pressure of liquid A was found to be $500$ torr. If the total vapor pressure of the mixture was $456$ torr, what is the vapor pressure of B$?$O a$.400$O b$.175$O c$.325$O d$.$ none of the choices e$.280$