Abreathing mixture used by deep-sea divers contains helium, oxygen, and carbon dioxide. what is the partial pressure of oxygen at 101.4kpa if p(he) = 68.7kpa and p(co2) = 1.4kpa?

Answer is: pressure of oxygen is 31,3 kPa.
The total pressure of an ideal gas mixture is the sum of the partial pressures of the gases in the mixture.
p(mixture) = p(helium) + p(oxygen) + p(carbon dioxide).
p(oxygen) = p(mixture) - (p(helium) + p(carbon dioxide)).
p(oxygen) = 101,4 kPa - (68,7 kPa + 1,4 kPa).
p(oxygen) = 101,4 kPa - 70,1 kPa.
p(oxygen) = 31,3 kPa.

Forgot the question hahaha