Lowest to greatest vapor pressure,

CH3CH2CH3 < CH3OC3 < CH3CH2OH< NaCl
the lower the boiling point the lower the vapour pressure. You can figure this out by deterring the types of forces present in the molecule and how strong they are. NaCl is an ionic bond and holds its molecules the closest so it is the highest. CH3CH2OH has hydrogen bonding but only on one side so it is the second highest. CH3OCH3 is small and compact and also has an Oxygen molecule in the centre making it some what polar. CH3CH2CH3 is the only non polar molecule that has just London forces and thus it would have the lowest vapour pressure. The greater the vapour pressure the higher the melting point so vapour pressure has to do with intermolecular forces.