Gas Law equation problem....?

Use Dalton's Law of Partial Pressures (P total = P1 + P2 + P3...) to solve - the total pressure is equal to the sum of the pressures of the individual gases in the mixture. The mixture is O2 and H2O. If the total pressure is 676 torr, and the pressure of O2 is 30 torr, then the pressure of the H2O must be 676 - 30, or 646 torr.