To get the vapor pressure of the resulting solution, we use the Raoult’s Law:
Psolution = (χsolvent) (P°solvent)
1st: Calculate the mol fraction of the solvent. In this case, water is the solvent.
χsolvent = 3.7 mol / (3.7 mol + 0.6 mol)
χsolvent = 0.86
2nd: Calculate the vapor pressure.
Psolution = (0.86) (23.8 torr)
Psolution = 20.48 torr