Maybe your thinking too much about moles and mass.
Try looking at water's vapor pressure. Since you started with C and torr, I'll stay with those units. At 25 C, pure water has a vapor pressure of 23.8 torr.
In your problem, the salt water solution has a vapor pressure of 19.6 torr.
Why did the vapor pressure change? If you can answer that, you should be on your way to the correct answer.